Oil-based ink for preparation of printing plate by ink jet process and method for preparation of printing plate using the same

ABSTRACT

A method is presented for preparing a lithographic printing plate by an ink jet process of discharging dropwise an oil-based ink using electrostatic attraction onto a lithographic printing plate precursor to form an image. The lithographic printing plate precursor has a water-resistant support having provided thereon an image-receiving layer having a lithographically printable hydrophilic surface for forming the image. The water-resistant support has a specific electric resistance of 10 10  Ωcm or less in an area directly under the image-receiving layer. The oil-based ink is composed of positively or negatively charged electroscopic resin particles dispersed in a nonaqueous carrier liquid having an electric resistance of 10 9  Ωcm or more and a dielectric constant of 3.5 or less. The resin particles are copolymer resin particles obtained by polymerization granulation of a solution of a monofunctional monomer, a monofunctional macromonomer and a resin for dispersion stabilization.

FILED OF THE INVENTION

The present invention relates to an oil-based ink for the preparation ofa printing plate by an ink jet process, and a method for the preparationof a printing plate by an ink jet process using the same. Moreparticularly, the present invention relates to an oil-based inkexcellent in dispersion stability, redispersibility, storage stability,image reproducibility and printing durability (press life), and a methodfor the preparation of a printing plate by an ink jet process using thesame.

BACKGROUND OF THE INVENTION

With development in business machines and progress in office automationin recent years, in the field of small-scale commercial printing,platemaking systems wherein an image is formed on a direct imaging typelithographic printing plate precursor comprising a water-resistantsupport having provided thereon an image receiving layer having ahydrophilic surface in a various manner to prepare an offsetlithographic printing plate have been widely employed.

A conventional lithographic printing plate precursor for direct imagingtype comprises a support made of paper subjected to water-resistanttreatment or a plastic film having provided thereon an image acceptinglayer (or an image receiving layer) containing an inorganic pigment, awater-soluble resin and a water resistance imparting agent. On such adirect imaging type lithographic printing plate precursor, a lipophilicimage is formed with a typewriter or by hand writing, using a lipophilicink, or by transferring an image from an ink ribbon by heat melting witha heat transfer printer, thereby preparing a printing plate.

However, the printing plate prepared by such a method is not sufficientin mechanical strength of image areas, so that cutting easily takesplace in the image areas during printing.

On the other hand, ink jet recording is a recording method low in noiseand printable at a high speed, and has recently been rapidlypopularized.

As such ink jet recording methods, there are proposed various systemssuch as a so-called electric field controlling system in which ink isdischarged using electrostatic attraction, a so-called drop-on-demandsystem (pressure pulse system) in which ink is discharged usingoscillation pressure of a piezoelectric element, and a so- called bubble(thermal) jet system in which ink is discharged using pressure generatedby forming bubbles and allowing them to grow up with heating at hightemperature. According to these systems, highly accurate images can beobtained.

In these ink jet recording systems, aqueous ink using water as a mainsolvent, and oil-based ink using an organic solvent as a main solventare conventionally employed.

It is also known that plate making is performed using an ink jet printeron a lithographic printing plate precursor for direct imaging typedescribed above. In this case, although aqueous ink in which water isused as a dispersion medium is employed, the aqueous ink has theproblems in that blurs appear in images formed on the precursor and inthat an image drawing speed is decreased because of slow drying. Inorder to overcome such problems, a method using oil-based ink in which anonaqueous solvent is used as a dispersion medium is proposed asdescribed in JP-A-54-117203 (the term "JP-A" as used herein means an"unexamined published Japanese patent application").

However, this method is still insufficient, because blurs are actuallyobserved in images formed by plate making and further blurs aregenerated in prints upon printing. Further, the number of printsobtained is limited to several hundreds at the most. Moreover, such inkhas the problem of being liable to clog a nozzle for discharging minuteink droplets which make it possible to obtain images having highresolution by the plate making.

In the ink jet recording systems, ink is usually passed through a filterand discharged from a nozzle, so that abnormal discharge of ink tends totake place by clogging of the nozzle or the filter, change in fluidityof the ink with the lapse of time, or various other factors.

This abnormal discharge of ink occurs not only with an aqueous inkcomposition, but also with an oil-based ink composition. Variousproposals for controlling the abnormal discharge of ink have been made.For example, in order to prevent the abnormal discharge of ink in caseof using an oil-based ink composition, it is proposed that the viscosityand specific resistance of the ink composition is controlled asdescribed in JP-A-49-50935, for the ink jet recording method of theelectric field controlling system. It is also proposed that thedielectric constant and specific resistance of the solvent used in theink composition are controlled as described in JP-A-53-29808.

Furthermore, as attempts to prevent clogging of nozzles caused byordinary oil-based ink for ink jet printer, there are proposed, forexample, methods in which dispersion stability of pigment particles isimproved (e.g., JP-A-4-25573, JP-A-5-25413 and JP-A-5-65443) and methodsin which specific compounds are incorporated into ink compositions(e.g., JP-A-3-79677, JP-A-3-64377, JP-A-4-202386 and JP-A-7-109431).

However, when these ink compositions are used for image formation oflithographic printing plate, the images formed are poor in imagestrength during printing, and the resulting printing plate cannot have asufficient press life.

SUMMARY OF THE TNVENTION

An object of the present invention is to provide an oil-based ink forthe preparation of a printing plate by an ink jet process which isexcellent in dispersion stability, redispersibility, storage stability,image reproducibility and press life.

Another object of the present invention is to provide an oil-based inkfor the preparation of a printing plate by an ink jet process whichmakes it possible to provide many sheets of prints having clear images.

A further object of the present invention is to provide an oil-based inkfor the preparation of a printing plate by an ink jet process which doesnot induce clogging in a discharge part and in the course of ink supplyand which makes it possible to conduct stable discharge.

A still further object of the present invention is to provide a methodfor the preparation of a printing plate by an ink jet process whichmakes it possible to provide many sheets of prints having clear images.

Other objects of the present invention will become apparent from thefollowing description.

It has been found that these objects of the present invention areaccomplished by an oil-based ink for the preparation of a printing plateby an ink jet process comprising dropwise supplying an oil-based inkcomprising resin particles dispersed in a nonaqueous carrier liquidhaving an electric resistance of 10⁹ Ωcm or more and a dielectricconstant of 3.5 or less on a lithographic printing plate precursorcomprising a water-resistant support and a lithographically printablehydrophilic surface to form an image, wherein the resin particlesdispersed are copolymer resin particles obtained by polymerizationgranulation of a solution comprising (i), (ii) and (iii):

(i) at least one monofunctional monomer (A) which is soluble in anonaqueous solvent that is at least miscible with the nonaqueous carrierliquid and becomes insoluble in the nonaqueous solvent bypolymerization;

(ii) at least one monofunctional macromonomer (MA) having a weightaverage molecular weight of 2×10⁴ or less in which a polymerizabledouble bond group represented by the formula (II) shown below isconnected with only one terminal of the main chain of a polymercomprising a repeating unit corresponding to a monomer and representedby the formula (I) shown below; ##STR1## wherein V⁰ represents --COO--,--OCO--, --(CH₂)_(r) COO--, --(CH₂)_(r) OCO--, --O--, --SO₂ --,--CONHCOO--, --CONHCONH--, --CON(D¹¹)--, --SO₂ N(D¹¹)-- or a phenylenegroup, in which D¹¹ represents a hydrogen atom or a hydrocarbon grouphaving from 1 to 22 carbon atoms, and r represents an integer of from 1to 4;

a¹ and a², which may be the same or different, each represents ahydrogen atom, a halogen atom, a cyano group, a hydrocarbon group,--COO--D¹² or --COO--D¹² linked through a hydrocarbon group, in whichD¹² represents a hydrogen atom or a hydrocarbon group which may besubstituted;

D⁰ represents a hydrocarbon group having from 8 to 22 carbon atoms or asubstituent having a total number of atoms of 8 or more, provided thathydrogen atoms directly attached to a carbon or nitrogen atom areexcluded from the number, represented by the following formula (Ia):

    .paren open-st.A.sup.1 -B.sup.1 .paren close-st..sub.m .paren open-st.A.sup.2 -B.sup.2 .paren close-st..sub.n D.sup.21  (Ia)

wherein D²¹ represents a hydrogen atom or a hydrocarbon group havingfrom 1 to 22 carbon atoms;

B¹ and B², which may be the same or different, each represents --O--,--CO--, --CO₂ --, --OCO--, --SO₂ --, --N(D²²)--, --CON(D²²)--, or--N(D²²)CO--, in which D²² has the same meaning as defined for D²¹above;

A¹ and A², which may be the same or different, each represents at leastone group selected from the group consisting of a group represented bythe formula (Ib) shown below and a hydrocarbon group having from 1 to 18carbon atoms, which each may be substituted, provided that, in the caseof two or more, it represents a combination of the group represented bythe formula (Ib) and/or the hydrocarbon group: ##STR2## wherein B³ andB⁴, which may be the same or different, each has the same meaning asdefined for B¹ or B² above;

A⁴ represents a hydrocarbon group having from 1 to 18 carbon atoms whichmay be substituted;

D²³ has the same meaning as defined for D²¹ above; and

m, n and p, which may be the same or different, each represents aninteger of from 0 to 4, provided that m and n are not 0 at the sametime; ##STR3## wherein V¹ represents --COO--, --CONHCOO--, --CONHCONH--,--CONH-- or a phenylene group; and

b¹ and b², which may be the same or different, each has the same meaningas defined for a¹ or a² in the formula (I);

(iii) at least one resin for dispersion stabilization (P) which issoluble in the nonaqueous solvent and comprises a copolymer componentrepresented by the formula (III) shown below: ##STR4## wherein R¹represents an alkyl group having from 10 to 32 carbon atoms or analkenyl group having from 10 to 32 carbon atoms;

d¹ represents a hydrogen atom or an alkyl group having from 1 to 4carbon atoms;

X¹ and X², which may be the same or different, each has the same meaningas defined for V⁰ in the formula (I);

W represents a group connecting X¹ and X² and comprising at least one ofa carbon atom and a hetero atom selected from an oxygen atom, a sulfuratom, a silicon atom and a nitrogen atom;

e¹, e², f¹ and f², which may be the same or different, each has the samemeaning as defined for a¹ or a² in the formula (I); and

x and y each represents a weight ratio of each repeating unit, xrepresents a number of from 90 to 99, y represents a number of from 10to 1, or a method for the preparation of a printing plate by an ink jetprocess comprising dropwise supplying the oil-based ink described aboveon a lithographic printing plate precursor comprising a water-resistantsupport and a lithographically printable hydrophilic surface to form animage.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. 1 is a schematic view showing one embodiment of a device system towhich the present invention can be applied.

FIG. 2 is a schematic view showing the main part of an ink jet recordingdevice which can be used in the present invention.

FIG. 3 is a partially sectional view showing a head of the ink jetrecording device which can be used in the present invention.

EXPLANATION OF THE SYMBOLS

    ______________________________________                                        1               Ink jet recording device                                        2 Master                                                                      3 Computer                                                                    4 Bus                                                                         5 Video camera                                                                6 Hard disk                                                                   7 Floppy disk                                                                 8 Mouse                                                                       10 Head                                                                       10a Discharge slit                                                            10b Discharge electrode                                                       10c Counter electrode                                                         11 Oil-based ink                                                              101 Upper unit                                                                102 Lower unit                                                              ______________________________________                                    

DETAILED DESCRIPTION OF THE INVENTION

The present invention is characterized in that the above-describedoil-based ink is discharged on a lithogrophic printing plate precursorby an ink jet process to form an image. The oil-based ink used isexcellent in dispersion stability, redispersibility and storagestability, and the resulting lithographic printing plate can provide alarge number of prints having clear images.

The present invention also includes the following embodiments.

(1) a method for the preparation of a printing plate by an ink jetprocess as described above, wherein the oil-based ink is dischargedusing electrostatic attraction.

(2) a method for the preparation of a printing plate by an ink jetprocess as described in (1) above, wherein the lithographic printingplate precursor comprises a water-resistant support having providedthereon an image receiving layer having a lithographically printablehydrophilic surface, and the support has a specific electric resistanceof 10¹⁰ Ωcm or less at least at an area directly under the imagereceiving layer.

(3) a method for the preparation of a printing plate by an ink jetprocess as described in (1) or (2) above, wherein the water-resistantsupport is a support having a specific electric resistance of 10¹⁰ Ωcmor less as a whole of the support.

(4) a method for the preparation of a printing plate by an ink jetprocess as described in (1), (2) or (3) above, wherein the resinparticles dispersed in the oil-based ink are electroscopic particlespositively or negatively charged.

Now, the present invention will be described in more detail below.

The oil-based ink for use in the present invention is described ingreater detail below.

The nonaqueous carrier liquid having an electric resistance of 10⁹ Ωcmor more and a dielectric constant of 3.5 or less used in the oil-basedink according to the present invention preferably includes a straightchain or branched chain aliphatic hydrocarbon, an alicyclic hydrocarbon,an aromatic hydrocarbon and halogen-substituted products thereof.Specific examples of the nonaqueous carrier liquid include octane,isooctane, decane, isodecane, decalin, nonane, dodecane, isododecane,cyclohexane, cyclooctane, cyclodecane, benzene, toluene, xylene,mesitylene Isopar E, Isopar G, Isopar H, Isopar L (Isopar: trade name ofExxon Co.), Shellsol 70, Shellsol 71 (Shellsol: trade name of Shell OilCo.), Amsco OME and Amsco 460 (Amsco: trade name of Spirits Co.), andmixtures thereof. The upper limit value of the electric resistance ofthe nonaqueous carrier liquid is about 10¹⁶ Ωcm, and the lower limitvalue of the dielectric constant thereof is about 1.80.

The nonaqueous dispersed resin particles (hereinafter also referred toas "latex particles"), which are the most important constituent in theoil-based ink of the present invention, are obtained by polymerizationgranulation in a nonaqueous solvent using at least one monofunctionalmonomer (A) and at least one monofunctional macromonomer (MA) in thepresence of a resin for dispersion stabilization (P) which is soluble inthe nonaqueous solvent and a random copolymer containing a polymercomponent having a double bond group copolymerizable with themonofunctional monomer (A).

As the nonaqueous solvent, those miscible with the nonaqueous carrierliquid of the above-described oil-based ink are basically usable.

Specifically, as the solvent used in the preparation of the dispersedresin particles, any solvent may be used as far as it is miscible withthe above-described carrier liquid. Preferred examples thereof include astraight chain or branched chain aliphatic hydrocarbon, an alicyclichydrocarbon, an aromatic hydrocarbon and halogen-substituted productsthereof. For example, hexane, octane, isooctane, decane, isodecane,decalin, nonane, dodecane, isododecane, Isopar E, Isopar G, Isopar H,Isopar L, Shellsol 70, Shellsol 71, Amsco OME and Amsco 460 can be usedindividually or as a mixture thereof.

Examples of a solvent which can be used by mixing together with thenonaqueous solvent include an alcohol (e.g., methyl alcohol, ethylalcohol, propyl alcohol, butyl alcohol, or a fluorinated alcohol), aketone (e.g., acetone, methyl ethyl ketone, or cyclohexanone), acarboxylic acid ester (e.g., methyl acetate, ethyl acetate, propylacetate, butyl acetate, methyl propionate, or ethyl propionate), anether (e.g., diethyl ether, dipropyl ether, tetrahydrofuran, or dioxane)and a halogenated hydrocarbon (e.g., methylene dichloride, chloroform,carbon tetrachloride, dichloroethane, or methylchloroform).

The solvent used together with the nonaqueous solvent is desirablyremoved by distillation under heating or a reduced pressure afterpolymerization granulation. However, even if it is introduced into theoil-based ink as a latex particle dispersion, no problem is encounteredas far as the requirements that the electric resistance of the ink is10⁹ Ωcm or more and that the dielectric constant thereof is 3.5 or lessare satisfied.

It is ordinarily preferred to employ a solvent same * as or similar tothe carrier liquid as described above in the stage of the preparation ofa resin dispersion. * Therefore, a straight chain or branched chainaliphatic hydrocarbon, an alicyclic hydrocarbon, an aromatic hydrocarbonand a halogenated hydrocarbon are preferably used.

The monofunctional monomer (A) for use in the present invention may beany monofunctional monomer as far as it is soluble in a nonaqueoussolvent, but insolubilized by polymerization. Specific examples thereofinclude a monomer represented by the following formula (IV): ##STR5##wherein T¹ represents --COO--, --OCO--, --CH₂ OCO--, --CH₂ COO--, --O--,--CONHCOO--, --CONHOCO--, --SO₂ --, --CON (W¹)--, --SO₂ N(W¹)-- or aphenylene group (phenylene group being hereinafter described as "--Ph--"sometimes, and including 1,2-, 1,3- and 1,4-phenylene groups), in whichW¹ represents a hydrogen atom or an aliphatic group having from 1 to 8carbon atoms which may be substituted (examples of the substituentincluding a halogen atom, a cyano group, an alkyl group, a hydroxygroup, or an alkoxy group having not more than 5 carbon atoms) (e.g.,methyl, ethyl, propyl, butyl, 2-chloroethyl, 2-bromoethyl, 2-cyanoethyl,2-hydroxyethyl, benzyl, chlorobenzyl, methylbenzyl, methoxybenzyl,phenethyl, 3-phenylpropyl, dimethylbenzyl, fluorobenzyl, 2-methoxyethyl,or 3-methoxypropyl);

D¹ represents a hydrogen atom or an aliphatic group having from 1 to 6carbon atoms which may be substituted (e.g., methyl, ethyl, propyl,butyl, 2-chloroethyl, 2,2-dichloroethyl, 2,2,2-trifluoroethyl,2-bromoethyl, 2-hydroxyethyl, 2-hydroxypropyl, 2,3-dihydroxypropyl,2-hydroxy-3-chloropropyl, 2-cyanoethyl, 3-cyanopropyl, 2-nitroethyl,2-methoxyethyl, 2-methanesulfonylethyl, 2-ethoxyethyl,N,N-dimethylaminoethyl, N,N-diethylaminoethyl, trimethoxysilylpropyl,3-bromopropyl, 4-hydroxybutyl, 2-furfurylethyl, 2-thienylethyl,2-pyridylethyl, 2-morpholinoethyl, 2-carboxyethyl, 3-carboxypropyl,4-carboxybutyl, 2-phosphoethyl, 3-sulfopropyl, 4-sulfobutyl,2-carboxyamidoethyl, 3-sulfoamidopropyl, 2-N-methylcarboxyamidoethyl,cyclopentyl, chlorocyclohexyl, or dichlorohexyl); and

g¹ and g², which may be the same or different, each has the same meaningas defined for a¹ or a² in the formula (I).

Specific examples of the monofunctional monomer (A) include a vinylester or allyl ester of an aliphatic carboxylic acid having from 1 to 6carbon atoms such as acetic acid, propionic acid, butyric acid,monochloroacetic acid, or trifluoropropionic acid; an alkyl ester oramide having from 1 to 4 carbon atoms which may be substituted of anunsaturated carboxylic acid such as acrylic acid, methacrylic acid,crotonic acid, itaconic acid or maleic acid (the alkyl group including,for example, methyl, ethyl, propyl, butyl, 2-chloroethyl, 2-bromoethyl,2-fluoroethyl, trifluoroethyl, 2-hydroxyethyl, 2-cyanoethyl,2-nitroethyl, 2-methoxyethyl, 2-methanesulfonylethyl,2-benzenesulfonylethyl, 2-(N,N-dimethylamino)ethyl,2-(N,N-diethylamino)ethyl, 2-carboxyethyl, 2-phosphoethyl,4-carboxybutyl, 3-sulfopropyl, 4-sulfobutyl, 3-chloropropyl,2-hydroxy-3-chloropropyl, 2-furfurylethyl, 2-pyridinylethyl,2-thienylethyl, trimethoxysilylpropyl and 2-carboxyamidoethyl); astyrene derivative (e.g., styrene, vinyl-toluene, α-methylstyrene,vinylnaphthalene, chlorostyrene, dichlorostyrene, bromostyrene,vinylbenzenecarboxylic acid, vinylbenzenesulfonic acid,chloromethylstyrene, hydroxymethylstyrene, methoxymethylstyrene,N,N-dimethylaminomethylstyrene, vinylbenzenecarboxyamide, orvinylbenzenesulfoamide); an unsaturated carboxylic acid (e.g., acrylicacid, methacrylic acid, crotonic acid, maleic acid or itaconic acid); acyclic acid anhydride of maleic acid or itaconic acid; an acrylonitrile;a methacrylonitrile; and a heterocyclic compound having a polymerizabledouble bond group (for example, compounds described in "Polymer DataHandbook, --Fundamental Volume--", edited by Kobunshi Gakkai, pages 175to 184, Baifukan (1986), specifically, N-vinylpyridine,N-vinylimidazole, N-vinylpyrrolidone, vinyl-thiophene,vinyltetrahydrofuran, vinyloxazoline, vinyl-thiazole, orN-vinylmorpholine).

Two or more kinds of monomers (A) may be used in combination.

The monofunctional macromonomer (MA) for use in the present invention isdescribed in more detail below.

The monofunctional macromonomer (MA) is a macro-monomer having a weightaverage molecular weight of 2×10⁴ or less in which a polymerizabledouble bond group represented by the formula (II) is connected with onlyone terminal of the main chain of a polymer comprising a repeating unitrepresented by the formula (I).

In the formulas (I) and (II), hydrocarbon groups contained in a¹, a²,V⁰, D⁰, b¹ and b² each has the number of carbon atoms as shown above (asan unsubstituted hydrocarbon group), and they may be substituted, forexample, with a halogen atom, an acyl group, an amino group, a cyanogroup, an alkoxy group, an aryl group which may be substituted with analkyl or haloalkyl group, or an amido group.

In the formula (I), D¹¹ in the substituent represented by V⁰ representsa hydrocarbon atom, as well as a hydrogen atom. Preferred examples ofthe hydrocarbon group include an alkyl group having from 1 to 22 carbonatoms which may be substituted (for example, methyl, ethyl, propyl,butyl, heptyl, hexyl, octyl, nonyl, decyl, dodecyl tridecyl, tetradecyl,hexadecyl, octadecyl, eicosanyl, docosanyl, 2-chloroethyl, 2-bromoethyl,2-cyanoethyl, 2-methoxycarbonylethyl, 2-methoxyethyl and 3-bromopropyl),an alkenyl group having from 4 to 18 carbon atoms which may besubstituted (for example, 2-methyl-1-propenyl, 2-butenyl, 2-pentenyl,3-methyl-2-pentenyl, 1-pentenyl, 1-hexenyl, 2-hexenyl,4-methyl-2-hexenyl, decenyl, dodecenyl, tridecenyl, hexadecenyl,octadecenyl and linoleyl), an aralkyl group having from 7 to 12 carbonatoms which may be substituted (for example, benzyl, phenetyl,3-phenylpropyl, naphthyl- methyl, 2-naphthylethyl, chlorobenzyl,bromobenzyl, methyl- benzyl, ethylbenzyl, methoxybenzyl, dimethylbenzyland dimethoxybenzyl), an alicyclic group having from 5 to 8 carbon atomswhich may be substituted (for example, cyclohexyl, 2-cyclohexylethyl and2-cyclopentylethyl), and an aromatic group having from 6 to 12 carbonatoms which may be substituted (for example, phenyl, naphthyl, tolyl,xylyl, propylphenyl, butylphenyl, octylphenyl, dodecylphenyl,methoxyphenyl, ethoxyphenyl, butoxyphenyl, decyloxyphenyl, chlorophenyl,dichlorophenyl, bromophenyl, cyanophenyl, acetylphenyl,methoxycarbonylphenyl, ethoxycarbonylphenyl, butoxycarbonylphenyl,acetamidophenyl, propionamidophenyl and dodecyloylamidophenyl).

When V⁰ represents --Ph-- (a phenylene group), a benzene ring may haveone or more substituents. The substituent includes a halogen atom (forexample, chlorine and bromine) and an alkyl group (for example, methyl,ethyl, propyl, butyl, chloromethyl and methoxymethyl).

a¹ and a², which may be the same or different, each preferablyrepresents a hydrogen atom, a halogen atom (for example, chlorine orbromine), a cyano group, an alkyl group having from 1 to 3 carbon atoms(for example, methyl, ethyl or propyl), --COO--D¹³ or --CH₂ COO--D¹³(wherein D¹³ represents a hydrogen atom or an alkyl, alkenyl, aralkyl,alicyclic or aryl group having from 1 to 18 carbon atoms, which may besubstituted, and specific examples thereof are the same as thosedescribed for D¹¹ above).

When D⁰ represents a hydrocarbon group having from 8 to 22 carbon atoms,specific examples thereof are the same as those described for D¹¹ above.

The case where D⁰ represents a substituent having a total number ofatoms of 8 or more (excluding hydrogen atoms directly attached to acarbon or nitrogen atom) represented by the formula (Ia) is described indetail below.

A¹ and A² each represents at least one group selected from a grouprepresented by the formula (Ib) and a hydrocarbon group having from 1 to18 carbon atoms (examples of the hydrocarbon group include an alkylgroup, an alkenyl group, an aralkyl group and an alicyclic group, andspecific examples thereof include those described for D¹¹ above) (in thecase of two or more, each represents an appropriate combination of thegroup of the formula (Ib) and/or the hydrocarbon group).

More specifically, examples of A¹ and A² include any appropriatecombinations of atomic groups such as --C(D³¹)(D³²)-- (in which D³² andD³² each represents a hydrogen atom, an alkyl group or a halogen atom),--(CH═CH)--, a phenylene group (--Ph--), a cyclohexylene group(cyclohexylene group being hereinafter described as "--C₆ H₁₀ --"sometimes, and including 1,2-, 1,3- and 1,4-cyclohexylene groups) andthe group represented by the formula (Ib) above.

When D⁰ represents the substituent having a total number of atoms of 8or more represented by the formula (Ia), it is preferred that a"connecting main chain" composed of from V⁰ to D²¹ (namely, V⁰, A¹ B¹,A², B² and D²¹) in a connecting group of (--V⁰ .paren open-st.A¹ -B¹.paren close-st._(m) .paren open-st.A² -B² .paren close-st._(n) D²¹) inthe formula (I) has a total number of atoms of 8 or more.

The number of atoms constituting the "connecting main chain" means that,for example, when V⁰ represents --COO-- or --CONH--, the oxo group (═Ogroup) and the hydrogen atom are not contained in the number of atoms,and the carbon atom, the ether type oxygen atom and the nitrogen atomconstituting the connecting main chain are contained in the number ofatoms (which is different from the total number of atoms defined in D⁰).Accordingly, with respect to --COO-- and --CONH--, the number of atomsis counted as 2. At the same time, when D²¹ represents --C₉ H₁₉, thehydrogen atoms are not contained in the number of atoms, and the carbonatoms are contained therein. In this case, therefore, the number ofatoms is counted as 9.

Further, when A and A each has the group represented by the formula(Ib), a group of (--B³ .paren open-st.A⁴ --B⁴ .paren close-st._(p) D²³)is also included in the above-described "connecting main chain".

In the repeating unit corresponding to a monomer and represented by theformula (I), specific examples of the repeating units in the case whereD⁰ represents the substituent represented by the formula (Ia), that is,two or more specific polar groups are contained in the repeating unitare set forth below.

In the following formulas (1) to (19), each symbol donates thefollowing:

    r.sub.1 : --H, --CH.sub.3, --Cl or --CN

    r.sub.2 : --H or --CH.sub.3

    λ: an integer of from 2 to 10

    p: an integer of from 2 to 6

    q: an integer of from 2 to 4

    m: an integer of from 1 to 12

    n: an integer of from 4 to 18 ##STR6##

The macromonomer (MA) used in the present invention has a chemicalstructure in which a polymerizable double bond group represented by theformula (II) is connected with only one terminal of the main chain of apolymer comprising a repeating unit corresponding to a monomer andrepresented by the formula (I), directly or through an appropriateconnecting group, as described above.

In the formula (II), V¹ represents --COO--, --CONHCOO--, --CONHCONH--,--CONH-- or a phenylene group.

Specific examples of the phenylene group are the same as those of thephenylene group described for V⁰ in the formula (I). b¹ and b², whichmay be the same or different, each has the same meaning as defined fora¹ or a² in the formula (I), and specific examples thereof are the sameas those described for a¹ and a².

It is more preferred that either of b¹ and b² in the formula (II) is ahydrogen atom.

A group connecting a component of formula (I) to a component of formula(II) is constituted by any combination of atomic groups of a carbonatom-carbon atom bond (either a single bond or a double bond), a carbonatom-hetero atom bond (examples of the hetero atom include an oxygenatom, a sulfur atom, a nitrogen atom and silicon atom) and a heteroatom-hetero atom bond.

Of the macromonomers (MA) according to the present invention, thoserepresented by the following formula (V) are preferred. ##STR7## whereinsymbols other than Z have the same meanings as defined for those in theformulas (I) and (II), respectively.

Z represents a single bond, an individual connecting group selected fromatomic groups such as --C(D⁴¹)(D⁴² )-- (in which D⁴¹ and D⁴² eachrepresents a hydrogen atom, a halogen atom (for example, fluorine,chlorine or bromine), a cyano group, a hydroxyl group, an alkyl group(for example, methyl, ethyl or propyl)), --(CH═CH)--, --C₆ H₁₀ --, (acyclohexylene group), --Ph-- (a phenylene group), --O--, --S--, --CO--,--N(D⁴³)--, --COO--, --SO--, --CON(D⁴³)--, --SON(D⁴³)--, --NHCOO--,--NHCONH--, --Si(D⁴³)(D⁴⁴)-- (in which D⁴³ and D⁴⁴ each represents ahydrogen atom or a hydrocarbon group having the same meaning as definedfor D¹¹ described above), ##STR8## or a connecting group constituted byan appropriate combination of two or more thereof.

In the formula (V), particularly preferred examples of a¹, a², b¹, b²,V⁰ and V¹ are shown, respectively, below.

V⁰ includes --COO--, --OCO--, --O--, --CH₂ COO-- and --CH₂ OCO--; V¹includes all the groups described above; and a¹, a², b¹ and b² include ahydrogen atom and a methyl group, respectively.

Specific examples of a moiety represented by the formula (II') shownbelow in the macromonomer of the formula (V) are set forth below, butthe present invention should not be construed as being limited thereto.##STR9##

In the following, b represents --H or --CH₃ ; ml represents an integerof from 1 to 12; and n1 represents an integer of from 2 to 12. ##STR10##

Furthermore, the macromonomer (MA) used in the present invention maycontain other repeating unit(s) as copolymerization component(s)together with the repeating unit corresponding to a monomer andrepresented by the formula (I).

Such other copolymerization components may be any compounds, as long asthey are monomers copolymerizable with the monomer corresponding to therepeating unit of the formula (I). Examples thereof include anunsaturated carboxylic acid such as acrylic acid, methacrylic acid,itaconic acid, crotonic acid, maleic acid, vinylacetic acid and4-pentenoic acid, an ester or amide of these unsaturated carboxylicacids, a vinyl ester or allyl ester of a fatty acid having from 1 to 22carbon atoms, a vinyl ether, a styrene and styrene derivative and aheterocyclic compound containing a polymerizable double bond group.

Specific examples thereof include the compounds illustrated as exampleswith respect to the monomers (A) described above, but are not limitedthereto.

In the macromonomer (MA), a component of the repeating unit representedby the formula (I) is contained preferably in an amount of 60% by weightor more, and more preferably in an amount of 80% to 100% by weight, ofthe total amount of the repeating units contained therein.

The macromonomer (MA) of the present invention has preferably a weightaverage molecular weight of from 1×10³ to 2×10⁴, more preferably from3×10³ to 1.5×10⁴.

The macromonomer (MA) of the present invention can be produced byconventionally known synthesis methods. Examples thereof include (1) amethod by ionic polymerization in which various reagents are reactedwith a terminal of a living polymer obtained by anionic polymerizationor cationic polymerization to form a macromonomer; (2) a method byradical polymerization in which various reagents are reacted with anoligomer having a terminal reactive group obtained by radicalpolymerization using a polymerization initiator and/or chain transferagent containing a reactive group such as a carboxyl, hydroxy or aminogroup in its molecule, thereby forming a macromonomer; and (3) a methodby polyaddition condensation in which a polymerizable double bond groupis introduced into an oligomer obtained by a polyaddition orpolycondensation reaction, in the same manner as in the above-describedradical polymerization.

Specifically, the macromonomer can be synthesized according to methodsdescribed, for example, in P. Dreyfuss & R. P. Quirk, Encycl. Polym.Sci. Eng., 7, 551 (1987), P. F. Rempp & E. Franta, Adv. Polym. Sci., 58,1 (1984), V. Percec, Appl. Polym. Sci., 285, 95 (1984), R. Asami & M.Takari, Makromol. Chem. Suppl., 12, 163 (1985), P. Rempp et al.,Makromol. Chem. Suppl., 8, 3 (1984), Yusuke Kawakami, Kagaku Kogyo, 38,56 (1987), Yuya Yamashita, Kobunshi, 31,988 (1982), Shiro Kobayashi,Kobunshi, 30, 625 (1981), Toshinobu Higashimura, Nippon SetchakuKyokaishi, 11, 536 (1982), Koichi Ito, Kobunshi Kako, 35, 262 (1986) andKishiro Azuma & Takashi Tsuda, Kino Zairyo, 10, 5 (1987), and literaturereferences and patents cited therein.

Examples of the polymerization initiator containing a reactive group inits molecule described above include an azobis compound, such as4,4'-azobis(4-cyanovaleric acid), 4,4'-azobis(4-cyanovaleric acidchloride), 2,2'-azobis(2-cyanopropanol), 2,2'-azobis(2-cyanopentanol),2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide],2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)ethyl]propionamide},2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide},2,2'-azobis(2-amidinopropane),2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide],2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane],2,2'-azobis[2-(4,5,6,7-tetrahydro-1H-1,3-diazepin-2-yl)propane],2,2'-azobis[2-(3,4,5,6,-tetrahydropyrimidin-2-yl)propane],2,2'-azobis[2-(5-hydroxy-3,4,5,6,-tetrahydropyrimidin-2-yl)propane],2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane},2,2'-azobis[N-(2-hydroxyethyl)-2-methylpropionamidine] and2,2'-azobis[N-(4-aminophenyl)-2-methylpropionamidine].

Further, examples of the chain transfer agent containing a specificreactive group in its molecule include a mercapto compound containingthe reactive group or a substituent capable of being derived to thereactive group (for example, thioglycolic acid, thiomalic acid,thiosalicylic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid,3-mercaptobutyric acid, N-(2-mercaptopropionyl)glycine,2-mercaptonicotinic acid, 3-[N-(2-mercaptoethyl)carbamoyl]propionicacid, 3-[N-(2-mercaptoethyl)amino]propionic acid,N-(3-mercaptopropionyl)alanine, 2-mercaptoethanesulfonic acid,3-mercaptopropanesulfonic acid, 4-mercaptobutanesulfonic acid,2-mercaptoethanol, 3-mercapto-1,2-propanediol, 1-mercapto-2-propanol,3-mercapto-2-butanol, mercaptophenol, 2-mercaptoethylamine,2-mercaptoimidazole and 2-mercapto-3-pyridinol) and an iodinated alkylcompound containing the reactive group or a substituent capable of beingderived to the reactive group (for example, iodoacetic acid,iodopropionic acid, 2-iodoethanol, 2-iodoethanesulfonic acid and3-iodopropanesulfonic acid). Preferred examples thereof include mercaptocompounds.

The amounts of the chain transfer agent and the polymerization initiatorused are preferably from 0.5 to 20 parts by weight, and more preferablyfrom 1 to 10 parts by weight, based on 100 parts by weight of the totalmonomers, respectively.

The dispersed resin according to the present invention comprises atleast one monomer (A) and at least one monofunctional macromonomer (MA).It is important that the resin synthesized from these monomers isinsoluble in a nonaqueous solvent, whereby the desired dispersed resincan be obtained.

More specifically, the monofunctional macromonomer (MA) is usedpreferably in an amount of from 0.1% to 20% by weight, and morepreferably from 0.3% to 15% by weight, based on the monomer (A) to beinsolubilized.

Within the ranges as described above, the dispersed resin particles ofthe oil-based ink of the present invention are excellent in dispersionstability, redispersibility and storage stability. Also, rapid fixingproperty after the image formation is good, the image formed is wellretained during printing and good press life is achieved.

The resin for dispersion stabilization (P) according to the presentinvention which is employed for making a polymer insoluble in thenonaqueous solvent formed by polymerization of the monomers a stableresin dispersion in the nonaqueous solvent is described in detail below.

The resin for dispersion stabilization (P) according to the presentinvention is a random copolymer soluble in the nonaqueous solventcontaining a copolymer component which works for solubilizing the randomcopolymer in the nonaqueous solvent (hereinafter referred to component Xsometimes) and a copolymer component having a double bond groupcopolymerizable with the monomer (A) at a terminal of the side chainthereof (hereinafter referred to component Y sometimes) each representedby the formula (III) described above.

Two or more kinds of the component X may be contained in the resin fordispersion stabilization (P) according to the present invention.

In the formula (III), R¹ represents an alkyl group having from 10 to 32carbon atoms or an alkenyl group having from 10 to 32 carbon atoms, eachof which may be a straight chain or a branched chain. Specific examplesthereof include a decyl group, a dodecyl group, a tridecyl group, atetradecyl group, a pentadecyl group, a hexadecyl group, an octadecylgroup, an eicosanyl group, a docosanyl group, a decenyl group, adodecenyl group, a tridecenyl group, a hexadecenyl group, an octadecenylgroup, an eicosenyl group, docosenyl group, and a linoleyl group.

d¹ represents a hydrogen atom or an alkyl group having from 1 to 4carbon atoms (e.g., methyl, ethyl, propyl, or butyl), and preferably ahydrogen atom or a methyl group.

X¹ and X², which may be the same or different, each has the same meaningas defined for V⁰ in the formula (I).

W represents a group connecting X¹ and X² and comprising at least one ofa carbon atom and a hetero atom selected from an oxygen atom, a sulfuratom, a silicon atom and a nitrogen atom.

The connecting group includes a carbon atom-carbon atom bond (either asingle bond or a double bond), a carbon atom-hetero atom bond (thehetero atom including an oxygen atom, a sulfur atom, a nitrogen atom anda silicon atom), a hetero atom-hetero atom bond, a heterocyclic groupand an appropriate combination thereof. Specific examples thereofinclude ##STR11## wherein r₃, r₄, r₅ and r₆, which may be the same ordifferent, each represents a hydrogen atom, a halogen atom (e.g.,fluorine, chlorine, or bromine), a cyano group, a hydroxy group or analkyl group (e.g., methyl, ethyl, or propyl);

r₇, r₈ and r₉, which may be the same or different, each represents ahydrogen atom or an alkyl group (e.g., methyl, ethyl, propyl, or butyl);and

r₁₀ and r₁₁, which may be the same or different, each represents ahydrogen atom, a hydrocarbon group having from 1 to 8 carbon atoms(e.g., methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, phenethyl,phenyl, or tolyl) or --Or₁₂ (wherein r₁₂ represents a hydrocarbon grouphaving from 1 to 8 carbon atoms (e.g., methyl, ethyl, propyl, butyl,pentyl, hexyl, benzyl, phenethyl, phenyl, or tolyl)).

The heterocyclic group for the connecting group is derived from aheterocyclic ring containing a hetero atom, for example, an oxygen atom,a sulfur atom or a nitrogen atom (e.g., thiophene, pyridine, pyrane,imidazole, benzimidazole, furan, piperidine, pyrazine, pyrrole, orpiperazine).

The connecting main chain group represented by --X¹ --W--X² -- containedin the component Y of the formula (III) preferably contains a totalnumber of atoms of 8 or more. The number of atoms constituting theconnecting chain group means that, for example, when X¹ represents--COO-- or --CONH--, the oxo group (═O) and the hydrogen atom are notcontained in the number of atoms, and the carbon atom, the ether typeoxygen atom and the nitrogen atom constituting the connecting main chaingroup are contained in the number of atoms. Therefore, in case of--COO-- or --CONH--, the number of atoms is counted as 2.

Specific examples of the component Y having a polymerizable double bondgroup are set forth below, but the present invention should not beconstrued as being limited thereto. In the following formulae (Y-1) to(Y-12), e¹ represents --H or <CH₃, e² represents --H, --CH₃, --Cl or--CN, k1 represents an integer of from 4 to 12, k2 represents an integerof from 2 to 6, L₁ represents ##STR12## --CH₂ CH═CH₂ or ##STR13##(wherein f¹ represents --H or --CH₃), and L₂ represents ##STR14## , or--CH₂ CH═CH₂ (wherein f² represents --CH₃, --Cl or --CN). ##STR15##

The resin for dispersion stabilization (P) according to the presentinvention can be easily prepared by means of conventionally knownsynthesis methods. More specifically, in order to introduce a copolymercomponent having a polymerizable double bond group (component Y), thereis a method in which a polymerization reaction is first conducted usinga monomer having a specific reactive group, for example, --OH, --COOH,--SO₃ H, --NH₂, --SH, --PO₃ H₂, --NCO, --NCS, --COCl, --SO₂ Cl or anepoxy group and a monomer corresponding to the component X in theformula (III), and then a reagent having a polymerizable double bondgroup is reacted with the resulting copolymer, thereby introducing thepolymerizable double bond group into the copolymer by a polymerreaction.

Specifically, the polymerizable double bond group can be introducedaccording to methods described, for example, in P. Dreyfuss & R. P.Quirk, Encycl. Polym. Sci. Eng., 7, 551 (1987), Yoshiki Nakajyo & YuyaYamashita, Senryo to Yakuhin, 30, 232 (1985), Akira Ueda & Susumu Nagai,Kagaku to Kogyo, 60, 57 (1986), P. F. Rempp & E. Franta, Advance inPolymer Science, 58, 1 (1984), Koichi Ito, Kobunshi Kako, 35, 262(1986), V. Percec, Applied Polymer Science, 2, 97 (1984), and literaturereferences cited therein.

Another method in which a bifunctional monomer having functional groupshaving different reactivity in a radical polymerization is subjected tocopolymerization reaction with a monomer corresponding to the componentX to prepare a copolymer represented by the formula (III) without theoccurrence of gelation as described in JP-A-60-185962 is also utilized.

In the resin represented by the formula (III), a weight ratio ofcomponent X/component Y is from 90/10 to 99/1, preferably from 92/8 to98/2. In such a range of the weight ratio, the occurrence of gelation inthe reaction mixture and the formation of coarse resin particles duringthe polymerization granulation reaction may be prevented, and thedispersion stability and redispersibility of the dispersed resinparticles are excellent.

The resin for dispersion stabilization (P) according to the presentinvention may contain, as a copolymer component, a repeating unit otherthan the repeating units corresponding to the components x and Yrespectively. The copolymer component to be included may be selectedfrom any monomers copolymerizable with the monomers corresponding to therepeating units shown in the formula (III). Such monomers, however, arepreferably employed in a range of not more than 20 parts by weight basedon 100 parts by weight of the total copolymer components. When theamount of other monomers exceeds the above-described range, thedispersion stability of the dispersed resin particles may tend todeteriorate.

The resin for dispersion stabilization (P) used in the present inventionis soluble in an organic solvent, and specifically, it is preferablydissolved in an amount of at least 5 parts by weight based on 100 partsby weight of toluene at a temperature of 25° C.

The weight average molecular weight (Mw) of the resin for dispersionstabilization (P) according to the present invention is preferably from2×10⁴ to 10×10⁶, more preferably from 3×10⁴ to 2×10⁵.

The dispersed resin particles used in the present invention aregenerally prepared by heat polymerization of the resin for dispersionstabilization (P), the monomer (A) and the macromonomer (MA) asdescribed above in the nonaqueous solvent in the presence of apolymerization initiator such as benzoyl peroxide,azobisisobutyronitrile or butyllithium. Specifically, there are (1) amethod of adding a polymerization initiator to a mixed solution of theresin for dispersion stabilization (P), the monomer (A) and themacromonomer (MA), (2) a method of adding dropwise the monomer (A) andthe macromonomer (MA) together with a polymerization initiator to asolution in which the resin for dispersion stabilization (P) isdissolved, (3) a method of adding a polymerization initiator and theremainders of the monomer (A) and the macromonomer (MA) to a mixedsolution containing the total amount of the resin for dispersionstabilization (P) and appropriate parts of the monomer (A) and themacromonomer (MA), and (4) a method of adding a mixed solution of theresin for dispersion stabilization (P), the monomer (A) and themacromonomer (MA) to a nonaqueous solvent together with a polymerizationinitiator. The dispersed resin particles can be prepared according toany of these methods.

The total amount of the monomer (A) and the macromonomer (MA) ispreferably from 10 parts to 100 parts by weight, more preferably from 10parts to 80 parts by weight, based on 100 parts by weight of thenonaqueous solvent.

The resin for dispersion stabilization (P) is used preferably in anamount of from 3 to 25 parts by weight, more preferably 5 to 20 parts byweight, based on 100 parts by weight of the total amount of themonomers.

The amount of the polymerization initiator is suitably from 0.1% to 10%by weight based on the total amount of monomers used. The polymerizationtemperature is preferably from about 40° C. to about 180° C., and morepreferably from 50° C. to 120° C. The reaction time is preferably from 3hours to 15 hours.

When the polar solvent described above, such as an alcohol, a ketone, anether or an ester is used in combination with the nonaqueous solventused in the reaction, or when unreacted monomers of the monomer (A) tobe subjected to polymerization granulation remain, it is preferred thatthe polar solvent or the unreacted monomers are removed by distillationunder heating to temperature equal to or higher than a boiling point ofthe solvent or the monomers, or under a reduced pressure.

The nonaqueous dispersed resin particles according to the presentinvention prepared as described above are present as particles which arevery fine and uniform in particle size distribution. The averageparticle size thereof is from 0.15 μm to 1.5 μm, more preferably from0.2 μm to 1.0 μm. The particle size can be determined using CAPA-500(trade name, manufactured by Horiba Ltd.).

The weight average molecular weight (Mw) of the dispersed resinaccording to the present invention is preferably from 5×10³ to 1×10⁶,more preferably from 8×10³ to 5×10⁵.

As to thermal properties, the dispersed resin according to the presentinvention has preferably a glass transition point ranging from 15° C. to80° C. or a softening point ranging from 35° C. to 1200C, preferably aglass transition point ranging from 20° C. to 60° C. or a softeningpoint ranging from 38° C. to 90° C.

The oil-based ink of the present invention is excellent in dispersionstability, redispersibility and storage stability. Also, rapid fixingproperty after image formation is good, the image formed is wellretained during printing, thereby exhibiting good press life.

More specifically, since it has very stable dispersibility, even when itis repeatedly used in a recording device for a long period of time, itis good in dispersibility and easily redispersed, so that contaminationdue to adhesion of the resin particles to each part of the device is notobserved at all.

Furthermore, due to its good fixing property, a strong coating is formedon the hydrophilic outermost surface of the lithographic printing plateprecursor by a rapid fixing treatment with heating after ink imageformation. This makes it possible to print a large number of sheets(good press life) in offset printing.

The oil-based ink of the present invention having the effects asdescribed above becomes available by a nonaqueous latex of the dispersedresin particles according to the present invention.

In the dispersed resin particles of the present invention, the resin fordispersion stabilization (P) is chemically bonded to the insoluble resinparticles at the time of polymerization granulation. The resin (P) whichis bonded to the resin particle is soluble in the nonaqueous solvent,and thus it brings about a so-called steric repulsion effect.

In addition, the macromonomer (MA) having the specific substituent iscopolymerized with the monomer (A) to be insolubilized at the time ofpolymerization granulation. The specific substituent moiety contained inthe macromonomer (MA) is designed so as to improve the affinity for thenonaqueous solvent, since particles are formed by nonaqueous dispersionpolymerization. It is therefore orientated in the interface (surface)area of the particle rather than it gets into the inside of theparticle, because of its good solvent affinity for the dispersionmedium. It is presumed that as a result, the affinity for the dispersionmedium on the particle surface is improved by using the macromonomer(MA) together with the resin for dispersion stabilization (P) tosignificantly enhance the effect of preventing aggregation of the resinparticles.

Consequently, it is believed that aggregation and precipitation of theinsoluble resin particles are inhibited, thereby remarkably improvingthe redispersibility.

It is preferred that the oil-based ink used in the present inventioncontains a coloring material as a color component for visual inspectionof a printing plate after plate making, in addition to theabove-described dispersed resin particles.

As the coloring material, any can be used as far as it is a pigment or adye conventionally employed in an oil-based ink or a liquid developerfor electrostatic photography.

The pigments which can be used include those ordinarily employed in thetechnical field of printing, regardless of inorganic pigments or organicpigments. Specifically, known pigments, for example, carbon black,cadmium red, molybdenum red, chrome yellow, cadmium yellow, TitanYellow, chromium oxide, pyridian, Titan Cobalt Green, ultramarine blue,Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments,quinacridone pigments, isoindolinone pigments, dioxazine pigments,threne pigments, perylene pigments, perynone pigments, thioindigopigments, quinophthalone pigments and metal complex pigments can be usedwithout particular limitation.

Preferred examples of the dyes include oil-soluble dyes, for example,azo dyes, metal complex dyes, naphthol dyes, anthraquinone dyes, indigodyes, carbonium dyes, quinoneimine dyes, xanthene dyes, cyanine dyes,quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes,naphthoquinone dyes, phthalocyanine dyes and metallophthalocyanine dyes.

These pigments and dyes may be used individually or in an appropriatecombination. They are preferably employed within the range of from 0.01%to 5% by weight based on the whole ink.

The coloring material may be dispersed by itself in the nonaqueoussolvent as dispersed particles, separately from the dispersed resinparticles, or incorporated into the dispersed resin particles. In orderto incorporate the coloring material into the dispersed resin particles,in general, pigments are coated with the resin material of the dispersedresin particles to form resin-coated particles, or the surface portionsof dispersed resin particles are colored with dyes to form coloredparticles.

Specifically, there is a method in which the dispersed resin is dyedwith an appropriate dye as described in JP-A-57-48738. Alternatively,there is a method in which the dispersed resin is chemically bonded to adye as described in JP-A-53-54029, or a method in which a monomerpreviously containing a dye is used at the time of polymerizationgranulation to form a dye-containing copolymer as described inJP-B-44-22955 (the term "JP-B" as used herein means an "examinedJapanese patent publication").

The dispersed resin particles and the colored particles (or coloringmaterial particles) contained in the oil-based ink of the presentinvention are preferably electroscopic particles positively ornegatively charged.

In order to impart the electroscopicity to the particles, the technologyof a liquid developer for electrostatic photography can be appropriatelyutilized. Specifically, it is carried out using an electroscopicmaterial, for example, a charge control agent and other additives asdescribed, for example, in "Recent Developments and Utilization ofElectrophotographic Development Systems and Toner Materials", pages 139to 148, "Fundamentals and Applications of ElectrophotographicTechniques", edited by Denshi Shashin Gakkai, pages 497 to 505 (Corona,1988), and Yuji Harazaki, "Electrophotography", 16 (No. 2), page 44(1977).

Suitable compounds are also described, for example, in British Patents893,429 and 934,038, U.S. Patents 1,122,397, 3,900,412 and 4,606,989,JP-B-4-51023, JP-B-6- 19595, JP-B-6-19596, JP-B-6-23865, JP-A-60-185963and JP-A-2-13965.

A charge control agent is preferably added in an amount of from 0.001part to 1.0 part by weight based on 1000 parts by weight of a dispersingmedium or a carrier liquid. various additives may be further added ifdesired, and the upper limit of the total amount of these additives isrestricted by the electric resistance of the oil-based ink.Specifically, if the electric resistance of the ink in a state ofexcluding the dispersed particles therefrom is lower than 109 Ωcm, itmay be difficult to obtain continuous gradation images of good quality.It is therefore desired to control the amount of each additive addedwithin the above described value of electric resistance.

The oil-based ink containing the electroscopic resin particles of thepresent invention is preferably employed in the ink jet recording methodof the electric field controlling system in which the ink is dischargedusing electrostatic attraction, since the discharge of the oil-based inkis easily performed.

Now, the method for the preparation of a lithographic printing plateaccording to the present invention is described in more detail below.

The lithographic printing plate precursor having a water-resistantsupport and a lithographically printable hydrophilic surface used in themethod of the present invention may be any as far as it provides ahydrophilic surface suitable for lithography.

The surface for receiving the ink image is a hydrophilic surfacepreferably having a contact angle with water of 5 degrees or less, morepreferably 0 degree, to provide prints without the generation of inkstains in the non-image areas.

Supports used for conventional offset printing plates having ahydrophilic surface are employed as they are. For example, an aluminumor aluminum alloy plate whose surface has been rendered hydrophilic or aplate comprising a water-resistant support having provided thereon analuminum or aluminum alloy layer whose surface has been renderedhydrophilic is used as the lithographic printing plate precursor of thepresent invention.

A lithographic printing plate precursor comprising a water-resistantsupport having provided thereon an image receiving layer having alithographically printable hydrophilic surface is preferably employed inthe present invention.

Examples of the water-resistant support include an aluminum plate, azinc plate, a bimetal plate (e.g., a copper-aluminum plate, acopper-stainless steel plate and a chromium-copper plate), and atrimetal plate (e.g., a chromium-copper-aluminum plate, achromium-lead-iron plate, and a chromium-copper-stainless steel plate)each preferably having a thickness of from 0.1 to 3 mm, particularlypreferably from 0.1 to 1 mm.

Also, paper subjected to water-resistant treatment, paper laminated witha plastic film or a metal foil, and a plastic film each preferablyhaving a thickness of from 80 μm to 200 μm are employed.

It is preferred that the water-resistant support haselectroconductivity, more specifically, a specific electric resistanceof 10¹⁰ Ωcm or less at least at an area directly under the imagereceiving layer. The specific electric resistance is more preferably 10⁸Ωcm or less. The smaller the specific electric resistance, the better.

In order to provide the above described specific electric resistance atleast in an area directly under the image receiving layer on a substratesuch as paper and a film, for example, a layer comprising anelectroconductive filler such as carbon black and a binder is appliedthereto, a metal foil is stuck thereon, or a metal is vapor- evaporatedthereon.

On the other hand, examples of the support having an electroconductivityas a whole include electroconductive paper impregnated, for example,with sodium chloride, a plastic film having an electroconductive fillersuch as carbon black incorporated therein, and a metal plate such as analuminum plate.

In the above-described range of electroconductivity, when ink dropletswhich have been charged attach to the image-receiving layer in ink jetrecording of the electric field controlling type, the charge of the inkdroplets is disappeared quickly through earth, and a clear image havingno disorder is formed.

In the present invention, the specific electric resistance (alsoreferred to as volume specific electric resistance or electricresistivity, sometimes) was measured by a three-terminal method using aguard electrode according to the method described in JIS K-6911.

The water-resistant support having electroconductivity as a whole usedin the present invention is described in more detail below.

For instance, the support is obtained by providing both sides of anelectroconductive paper obtained by impregnating sodium chloride into asubstrate with a water- resistant electroconductive layer.

In the present invention, the paper used for the substrate include woodpulp paper, synthetic pulp paper and mixed paper of wood pulp andsynthetic pulp. The thickness of the paper is preferably from 80 μm to200 μm.

The electroconductive layer is described in more detail below.

The electroconductive layer is formed by applying a compositioncontaining an electroconductive filler and a binder to both surfaces ofthe electroconductive paper. The thickness of the electroconductivelayer is preferably from 5 μm to 20 μm.

The electroconductive filler includes granulated carbon black, graphite,metal powder (e.g., silver powder, copper powder, nickel powder, brasspowder, aluminum powder, copper powder or stainless steel powder), tinoxide powder, aluminum flake, nickel flake, and carbon fiber.

A resin used for the binder can be appropriately selected from variousresins. Specifically, examples of the resin include a hydrophobic resin(e.g., acrylic resin, vinyl chloride resin, styrene resin,styrene-butadiene resin, styrene-acrylic resin, urethane resin,vinylidene chloride resin, and vinyl acetate resin) and a hydrophilicresin (e.g., polyvinyl alcohol resin, cellulose derivative, starch andderivatives thereof, polyacrylamide resin, and styrene-maleic anhydridecopolymer).

The electroconductive layer can be formed by laminating anelectroconductive thin film. Examples of the electroconductive thin filminclude a metal foil and an electroconductive plastic film. Morespecifically, the metal foil laminating material includes an aluminumfoil, and the electroconductive plastic film laminating materialincludes a polyethylene resin to which carbon black is incorporated. Thealuminum foil may be any of hard type and soft type, and the thicknessthereof is preferably from 5 μm to 20 μm.

The polyethylene resin laminate film containing carbon black ispreferably obtained using an extrusion laminating method. The methodcomprises melting polyolefin by heating, forming a film, immediatelypressing the film on paper, and cooling it for laminating. Variousapparatus are known for conducting the method. The thickness of thelaminate layer is preferably from 10 μm to 30 μm. As the support havingan electroconductivity as a whole, a plastic film having anelectroconductivity and a metal sheet can be used as they are as far asthe water-resistivity is satisfied.

The plastic film having an electroconductivity includes a polypropyleneor polyester film to which an electroconductive filler such as carbonfiber or carbon black is incorporated. The metal sheet includes analuminum sheet. The thickness of the substrate is preferably from 80 μmto 200 μm. If it is less than 80 μm, mechanical strength as a printingplate may be insufficient. On the other hand, if it exceeds 200 μm, ahandling property such as a transportability in a recording apparatusmay tend to decrease.

The support comprising a water-resistant substrate having providedthereon a layer having an electroconductivity is described in moredetail below.

As the water-resistant substrate, those described for thewater-resistant support above can be employed. In order to form anelectroconductive layer on the water- resistant substrate, the methodsas described in the formation of the support having anelectroconductivity as a whole can be used. Specifically, one surface ofthe substrate is coated with a layer containing an electroconductivefiller and a binder and having a thickness of from 5 μm to 20 μm, orlaminated with a metal foil or a plastic film having anelectroconductivity.

Furthermore, in addition to the methods described above, for example, avapor-evaporated film of a metal such as aluminum, tin, palladium orgold may be provided on a plastic film.

According to the methods described above, the water- resistant supporthaving a specific electric resistance of 10¹⁰ Ωcm or less as a whole ofthe support can be obtained.

As to the support used in the present invention, when an image receivinglayer is provided on the support, the smoothness of its surface on theside adjacent to the image receiving layer is adjusted to preferably atleast 300 (second/10 ml), more preferably from 900 to 3,000 (second/10ml) and particularly preferably from 1,000 to 3,000 (second/10 ml) inthe Bekk smoothness.

The Bekk smoothness can be measured with a Bekk smoothness tester. TheBekk smoothness tester is a tester for measuring a time required for adefinite amount (10 ml) of air to pass through between a test piece anda glass surface under a reduced pressure, wherein the test piece ispressed to a highly smoothly finished circular glass plate having a holeat its center at a definite pressure (1 kg/cm²).

The image reproducibility and the press life can be still more improvedby restricting the smoothness of the surface on the side adjacent to theimage receiving layer of the support to the above described value. Suchimproving effects are obtained even if the image receiving layer havingthe same surface smoothness is used, and it is considered that theincrease in the smoothness of the surface of the support has improvedadhesion between the image area and the image receiving layer.

The highly smooth surface of the water-resistant support thus restrictedmeans a surface directly coated with the image receiving layer.Therefore, for example, when the electroconductive layer describedabove, an under layer or an over-coat layer is provided on the support,it means the surface of the electroconductive layer, the under layer orthe over-coat layer.

Thus, the image receiving layer whose surface state is appropriatelyadjusted as described below is firmly held without being subjected tothe influence of unevenness of the surface of the support and as aresult, it makes possible to yet more improve the image quality.

The adjustment of the surface smoothness within the above-describedrange can be made using various known methods. Specifically, suchmethods include a method of melt-adhering a resin to a surface of asubstrate and a method of adjusting the Beck smoothness of a surface ofa support by calender reinforcement with a highly smooth hot roller.

Furthermore, in the present invention, the under layer can be providedbetween the support and the image receiving layer for improving thewater resistance and the interlayer adhesive quality as described above,and also a backcoat layer (back surface layer) can be provided on asurface of the support opposite to the image receiving layer forpreventing curling. It is preferred that the backcoat layer has asmoothness value ranging from 150 (second/10 ml) to 700 (second/10 ml)in the Bekk smoothness.

By providing such a backcoat layer on the support, when the printingplate obtained is supplied to an offset printing machine, the printingplate can be accurately mounted on the machine without the occurrence ofshears or slippage.

When the under layer and the backcoat layer of the support are eachadjusted to such a smoothness, it is preferred that the smoothness iscontrolled by repeating a calender treatment step plural times, forexample, by once conducting calender treatment after formation of theunder layer and conducting it again after formation of the backcoatlayer, or by a combination of the adjustment with respect tocompositions of the under layer and the backcoat layer described later,for example, the ratio and the grain size of a pigment, and theadjustment of calender treatment conditions.

The under layer and backcoat layer each is formed by coating and dryingor laminating a coating liquid containing a resin, a pigment or the likeon a support. The resin can be selected from various resinsappropriately. Specifically, they include those described for the above-described electroconductive layer.

Suitable examples of the pigment include clay, kaolin, talc, diatomearth, calcium carbonate, aluminum hydroxide, magnesium hydroxide,titanium oxide and mica. In order to attain the desired smoothness, thepigment is preferably used by appropriately selecting its grain size.For example, a relatively low smoothness is required in the backcoatlayer compared with the under layer, so that pigment having relatively alarge grain size, specifically, having a grain size of about 0.5 μm toabout 10 μm is preferably used. The pigment described above ispreferably used at a ratio of 80 parts to 200 parts by weight based on100 parts by weight of the resin in the backcoat layer. In order toobtain excellent water resistance, the under layer and the backcoatlayer effectively contain a water resistance imparting agent such as amelamine resin and a polyamide epichlorohydrin resin. The abovedescribed grain size can be measured using a scanning electronmicroscopic (SEM) photograph. When the grain is not spherical, the sizemeans a diameter determined by converting a projected area of the grainsto a circle and obtaining the equivalent circle.

In order to prepare the lithographic printing plate precursor used inthe present invention, generally, a solution containing components forthe under layer is applied onto one side of the support, followed bydrying to form the under layer, if necessary, a solution containingcomponents for the backcoat layer is further applied onto the other sideof the support, followed by drying to form the backcoat layer, ifnecessary, and subsequently, a coating solution containing componentsfor the image receiving layer is applied, followed by drying to form theimage receiving layer. The coating amount of the backcoat layer issuitably from 1 g/m² to 30 g/m², and preferably from 6 g/m² to 20 g/m².

More preferably, the thickness of the water-resistant support providedwith the under layer and/or the backcoat layer ranges suitably from 90μm to 130 μm, and preferably from 100 μm to 120 μm.

The image receiving layer is provided on the water-resistant support,and the thickness thereof is preferably from 5 μm to 50 μm.

The image receiving layer comprises, for example, a water-solublebinder, an inorganic pigment and a water-resistance imparting agent asits main component. The binder includes a water-soluble resin, forexample, PVA, modified PVA (e.g., carboxy modified PVA), starch and aderivative thereof, CMC, hydroxyethyl cellulose, casein, gelatin,polyvinylpyrrolidone, a copolymer of vinyl acetate and crotonic acid,and a copolymer of styrene and maleic acid.

Examples of the water resistance imparting agent includes glyoxal, aprimary condensation product of an aminoplasts such as a melamineformaldehyde resin or urea formaldehyde resin, a modified polyamideresin (e.g., methylol polyamide resin), and apolyamide-polyamine-epichlorohydrin resin. Examples of the inorganicpigment include kaolin, clay, calcium carbonate, silica, titanium oxide,zinc oxide, barium sulfate, and alumina. Among these, silica ispreferred.

In addition, the image receiving layer may contain a crosslinkingcatalyst such as ammonium chloride or a silane coupling agent.

In the present invention, the smoothness of the surface of the imagereceiving layer is preferably 50 (second/10 ml) or more, and morepreferably 80 (second/10 ml) or more, in the Bekk smoothness.

Defects and blurs of ink images which may be formed owing to theunevenness of the image receiving layer are preferably inhibited at theBekk smoothness of 50 or more.

A method for forming an image on the lithographic printing plateprecursor as described above (hereinafter also referred to as a"master") is described below. One example of a device system suitablefor performing such a method is shown in FIG. 1.

The device system shown in FIG. 1 comprises an ink jet recording device1 using an oil-based ink.

As shown in FIG. 1, pattern information of images (figures and letters)to be formed on a master 2 is first supplied from an information supplysource such as a computer 3 to the ink jet recording device 1 usingoil-based ink through a transmittal means such as a bus 4. A head forink jet recording 10 of the recording device 1 stores oil-based inktherein, and sprays fine droplets of the ink on the master 2 accordingto the above-described information, when the master 2 passes through inthe recording device 1, whereby the ink adheres to the master 2 inaccordance with the above-described pattern.

Thus, the image formation on the master 2 is completed to obtain aprinting plate.

Components of the ink jet recording device as shown in the device systemof FIG. 1 are shown in FIG. 2 and FIG. 3, respectively. In FIG. 2 andFIG. 3, members common to the members in FIG. 1 are designated using thesame symbols, respectively. FIG. 2 is a schematic view showing the mainpart of such an ink jet recording device, and FIG. 3 is a sectional viewshowing a part of the head.

The head 10 attached to the ink jet recording device has a slit betweenan upper unit 101 and a lower unit 102, a leading edge thereof forms adischarge slit 10a, a discharge electrode 10b is arranged in the slit,and the inside of the slit is filled with oil-based ink 11, as shown inFIG. 2 and FIG. 3.

In the head 10, voltage is applied to the discharge electrode 10baccording to a digital signal of pattern information of image. As shownin FIG. 2, a counter electrode 10c is provided opposite to the dischargeelectrode 10b, and the master 2 is placed on the counter electrode 10c.The application of voltage forms a circuit between the dischargeelectrode 10b and the counter electrode 10c, and the oil-based ink 11 isdischarged from the discharge slit 10a of the head 10, thereby formingimages on the master 2 placed on the counter electrode 10c.

It is preferred that the width of the discharge electrode 10b is asnarrow as possible in its leading edge, for forming images of highquality by the ink jet process.

For example, the head of FIG. 3 is filled with the oil-based ink, thedischarge electrode 10b whose leading edge has a width of 20 μm is used,the distance between the discharge electrode 10b and the counterelectrode 10c is adjusted to 1.5 mm, and a voltage of 3 KV is appliedbetween these electrodes for 0.1 millisecond, whereby print of a 40μm-dot can be formed on the master 2.

The oil-based ink according to the present invention is excellent indispersion stability, redispersibility, storage stability, imagereproducibility and printing durability (i.e., press life). The methodfor the preparation of a printing plate according to the presentinvention comprising image formation by an ink jet process using theoil-based ink according to the present invention provides a printingplate having excellent image reproducibility and printing durability ina simple manner.

The present invention will be described in greater detail with referenceto the following examples, but the present invention should not beconstrued as being limited thereto.

SYNTHESIS EXAMPLE 1 OF MACROMONOMER (MA) Synthesis of Macromonomer(MA-1)

A mixed solution of 100 g of octadecyl methacrylate, 2 g of3-mercaptopropionic acid and 200 g of toluene was heated to atemperature of 70° C. with stirring under nitrogen gas stream. To thesolution, 1.0 g of 2,2'-azobis(isobutyronitrile) (abbreviated as AIBN)was added to conduct a reaction for 4 hours, 0.5 g of AIBN was furtheradded to conduct the reaction for 3 hours, and 0.3 g of AIBN was stillfurther added to conduct the reaction for 3 hours. Then, 8 g of glycidylmethacrylate, 1.0 g of N,N-dimethyldodecylamine and 0.5 g oftert-butylhydroquinone were added to the reaction solution, and stirredat a temperature of 100° C. for 10 hours. After cooling, the reactionsolution was reprecipitated in 2 liters of methanol to obtain 82 g ofwhite powder. A weight average molecular weight (Mw) of the polymer was1×10⁴. The weight average molecular weight (Mw) was measured by GPCmethod and calculated in terms of polystyrene (hereinafter the same).

Macromonomer (MA-1) ##STR16##

SYNTHESIS EXAMPLES 2 to 11 OF MACROMONOMER (MA) Synthesis ofMacromonomers (MA-2) to (MA-11)

Macromonomers (MA-2) to (MA-11) were synthesized in the same manner asin Synthesis Example 1 of Macromonomer (MA) with the exception that onlyoctadecyl methacrylate is replaced by compounds corresponding to therepeating units shown in Table 1 below, respectively. The weight averagemolecular weight (Mw) of each macromonomer obtained was in a range offrom 9×10³ to 1×10⁴. ##STR17##

                  TABLE 1                                                         ______________________________________                                        Synthesis                                                                       Example                                                                       of Macro-                                                                     Macro- mono-                                                                  monomer mer                                                                   (MA) (MA) a.sub.1 /a.sub.2 X                                                ______________________________________                                          2 MA-2 --H/--CH.sub.3                                                          - 3 MA-3 --H/--CH.sub.3                                                                               #STR18##                                              - 4 MA-4 --H/--CH.sub.3                                                                               #STR19##                                              - 5 MA-5 --H/--H                                                                                      #STR20##                                              - 6 MA-6 --H/--CH.sub.3 --(CH.sub.2).sub.2 OCO(CH.sub.2).sub.2                                      COOC.sub.2 H.sub.5                                     7 MA-7 --H/--CH.sub.3 --(CH.sub.2).sub.2 OCO(CH.sub.2).sub.2 COOCH.sub.3      8 MA-8 --H/--H --(CH.sub.2).sub.2 OCOCH═CH--COOC.sub.5 H.sub.11                                    - 9 MA-9 --H/--H                                                              #STR21##                                              - 10  MA-10 --H/--CH.sub.3                                                                            #STR22##                                              - 11  MA-11 --H/--H --(CH.sub.2).sub.2 OCO(CH.sub.2).sub.2 SO.sub.2                                 C.sub.8 H.sub.17                                     ______________________________________                                    

SYNTHESTS EXAMPLE 12 OF MACROMONOMER (MA) Synthesis of Macromonomer(MA-12)

A mixed solution of 100 g of tetradecyl methacrylate, 2 g of thioethanoland 200 g of toluene was heated to a temperature of 70° C. with stirringunder nitrogen gas stream. To the solution, 1.0 g of AIBN was added toconduct a reaction for 4 hours, 0.5 g of AIBN was further added toconduct the reaction for 3 hours, and 0.3 g of AIBN was still furtheradded to conduct the reaction for 3 hours. The reaction solution wascooled to room temperature, and 8 g of 2-carboxyethyl acrylate was addedthereto. Then, a mixed solution of 12.7 g of dicyclohexylcarbodiimide(abbreviated as DCC) and 60 g of methylene chloride was added dropwisethereto over a period of 1 hour. Then, 1.0 g of tert-butylhydroquinonewas added, followed by stirring for 4 hours.

The crystals thus-deposited were removed by filtration, and the filtratewas reprecipitated in 2 liters of methanol. The precipitated oilyproduct was collected by decantation, dissolved in 150 ml of methylenechloride, and reprecipitated again in one liter of methanol. The oilyproduct was collected and dried under a reduced pressure to obtain apolymer having the Mw of 8×10³ in a yield of 60 g.

Macromonomer (MA-12) ##STR23##

SYNTHESTS EXAMPLE 13 to 15 OF MACROMONOMER (MA) Synthesis ofMacromonomer (MA-13) to (MA-15)

Macromonomers (MA-13) to (MA-15) shown in Table 2 below were synthesizedin the same manner as in Synthesis Example 12 of Macromonomer (MA) withthe exception that a methacrylate monomer (corresponding to tetradecylmethacrylate) and an unsaturated carboxylic acid (corresponding to2-carboxyethyl acrylate) were employed, respectively. The weight averagemolecular weight of each macromonomer obtained in a yield of 60 to 70 gwas in a range of from 7×10³ to 9×10³.

                                      TABLE 2                                     __________________________________________________________________________    Synthesis                                                                       Example                                                                       of Macro- Macro-                                                              monomer monomer Chemical Structure of Macromonomer                            (MA) (MA) (MA)                                                              __________________________________________________________________________      13 MA-13                                                                                 #STR24##                                                            - 14 MA-14                                                                              #STR25##                                                            - 15 MA-15                                                                             ##STR26##                                                         __________________________________________________________________________

SYNTHESIS EXAMPLE 16 OF MACROMONOMER (MA) Synthesis of Macromonomer(MA-16)

A mixed solution of 100 g of 2,3-dihexanoyloxypropyl methacrylate, 150 gof tetrahydrofuran and 50 g of isopropyl alcohol was heated to atemperature of 75° C. with stirring under nitrogen gas stream. To thesolution, 5.0 g of 4,4'-azobis(4-cyanovaleric acid) (abbreviated as ACV)was added to conduct a reaction for 5 hours, and then 1.0 g of ACV wasfurther added to conduct the reaction for 4 hours. After cooling, thereaction solution was reprecipitated in 1.5 liters of methanol, and theoily product was collected by decantation and dried under a reducedpressure. The yield was 85 g.

A mixture of 50 g of the resulting oily product, 15 g of glycidylmethacrylate, 1.0 g of N,N-dimethyldodecylamine, 1.0 g of2,2'-methylenebis(6-tert-butyl-p-cresol) and 100 g of toluene wasstirred at a temperature of 100° C. for 15 hours. After cooling, thereaction solution was reprecipitated in one liter of petroleum ether toobtain 63 g of white powder. The weight average molecular weight thereofwas 7x10³.

Macromonomer (MA-16) ##STR27##

SYNTHESIS EXAMPLE 1 OF RESIN FOR DISPERSION STABITTIZATION (P) Synthesisof Resin for Dispersion Stabilization (P-1)

A mixed solution of 96 g of octadecyl methacrylate, 4 g of4-(2-methacryloyloxyethyloxycarbonyl)butyric acid and 200 g of toluenewas heated to a temperature of 75° C. under nitrogen gas stream withstirring. To the solution was added 1.5 g of2,2'-azobis(isobutyronitrile) (abbreviated as AIBN) as a polymerizationinitiator, followed by reacting for 4 hours. Then, 0.8 g of AIBN wasadded to the reaction mixture, and the mixture was heated to atemperature of 80° C. and subjected to a reaction for 4 hours.

After cooling the reaction mixture to a temperature of 25° C., 6 g ofallyl alcohol was added with stirring and then a mixed solution of 10 gof dicyclohexylcarbodiimide (abbreviated as DCC), 0.1 g of4-(N,N-diethylamino)pyridine and 30 g of methylene chloride was dropwiseadded thereto over a period of one hour, followed by reacting for 3hours.

To the reaction mixture was added 10 g of a 80% aqueous solution offormic acid and the resulting mixture was stirred for one hour. Afterremoving the insoluble substance by filtration, the filtrate wasreprecipitated in 2.5 liters of methanol. The resulting precipitate wascollected by filtration and dissolved in 200 g of toluene. Afterremoving the insoluble substance by filtration, the filtrate wasreprecipitated in one liter of methanol. The resulting precipitate wascollected by filtration and dried to obtain 70 g of the desiredcopolymer. The weight average molecular weight (Mw) thereof was 5-10⁴.

Resin (P-1) ##STR28##

SYNTHESIS EXAMPLE 2 OF RESIN FOR DTSPERSION STABTLIZATION (P) Synthesisof Resin for Dispersion Stabilization (P-2)

A mixed solution of 50 g of dodecyl methacrylate, 45 g of octadecylacrylate, 5 g of glycidyl methacrylate and 200 g of toluene was heatedto a temperature of 75° C. under nitrogen gas stream with stirring. Tothe solution was added 1.8 g of AIBN, followed by reacting for 4 hours.Then, 0.5 g of AIBN was added to the reaction mixture, followed byreacting for 3 hours, and further 0.3 g of AIBN was added thereto,followed by reacting for 3 hours.

To the reaction mixture were added 6 g of 3-acryloyloxypropionic acid,1.0 g of N,N-dimethyldodecylamine and 0.5 g of tert-butylhydroquinone,and the mixture was stirred at a temperature of 100° C. for 10 hours.After cooling the reaction mixture, it was reprecipitated in 2 liters ofmethanol to obtain 82 g of the desired copolymer as white powder. Theweight average molecular weight (Mw) thereof was 4×10⁴.

Resin (P-2) ##STR29##

SYNTHESIS EXAMPLE 3 OF RESIN FOR DTSPERSION STABTLTZATION (P) Synthesisof Resin for Dispersion Stabilization (P-3)

A mixed solution of 96 g of tridecyl methacrylate, 4 g of11-methacrylamidoundecanoic acid and 200 g of toluene was heated to atemperature of 75° C. under nitrogen gas stream with stirring. To thesolution was added 1.0 g of AIBN, followed by reacting for 4 hours.Then, 0.5 g of AIBN was added to the reaction mixture, followed byreacting for 3 hours, and further 0.3 g of AIBN was added thereto,followed by reacting for 3 hours.

After cooling the reaction mixture to a temperature of 40° C., 0.2 g ofhydroquinone, then 6.9 g of vinyl acetate and 0.05 g of mercury acetatewere added thereto, followed by reacting for 2 hours. The temperaturethereof was again raised to 70° C., 7.5×10⁻³ ml of 100% of sulfuric acidwas added thereto and the mixture was reacted for 6 hours. To thereaction mixture was added 0.04 g of sodium acetate trihydrate, themixture was thoroughly stirred and poured into 4.5 liters of methanolfor reprecipitation and purification to obtain 75 g of the desiredcopolymer as slightly brownish viscous solid. The weight averagemolecular weight (Mw) thereof was 5.3×10⁴.

Resin (P-3) ##STR30##

SYNTHESIS EXAMPLE 4 OF RESIN FOR DISPERSION STABILIZATION (P) Synthesisof Resin for Dispersion Stabilization (P-4)

A mixed solution of 97 g of hexadecyl methacrylate, 3 g of Monomer (Y-1)having the structure shown below and 400 g of isodecane was heated to atemperature of 70° C. under nitrogen gas stream with stirring. To thesolution was added 1.5 g of 2,2'-azobis(isovaleronitrile) (abbreviatedas AIVN) as a polymerization initiator with stirring, followed byreacting for 4 hours. Then, 0.8 g of AIVN was added to the reactionmixture, followed by reacting for 3 hours, and further 0.5 g of AIVN wasadded thereto, followed by reacting for 3 hours. The solid content ofthe resulting reaction mixture was 19.9% by weight. The weight averagemolecular weight (Mw) of the copolymer obtained was 4>10⁴.

Monomer (Y-1) ##STR31## Resin (P-4) ##STR32##

PREPARATION EXAMPLE 1 OF RESIN PARTICLE Preparation of Resin Particle(L-1)

A mixed solution of 10 g of Resin for Dispersion Stabilization (P-1),100 g of vinyl acetate, 4 g of Macromonomer (MA-1) and 342 g of Isopar Hwas heated to a temperature of 70° C. under nitrogen gas stream withstirring. To the solution was added 1.5 g of2,2'-azobis(isovaleronitrile) (abbreviated as AIVN) as a polymerizationinitiator, followed by reacting for 3 hours and 0.8 g of AIVN wasfurther added, followed by reacting for 2 hours. Then, 0.5 g of AIBN wasadded to the reaction mixture and the mixture was heated to atemperature of 80° C., followed by reacting for 3 hours. The temperatureof the reaction mixture was raised to 100° C., followed by stirring for2 hours under a reduced pressure of 20 mmHg, thereby distilling off theunreacted monomers. After cooling the reaction mixture, it was passedthrough a nylon cloth of 200 mesh. The resulting white dispersion was alatex having a polymerization rate of 98% and an average particlediameter of 0.40 μm. The particle diameter was measured by CAPA-500manufactured by Horiba Ltd. (hereinafter the same).

A part of the above-described white dispersion was centrifuged at arotation of 1×10⁴ r.p.m. for one hour and the resin particlesprecipitated were collected and dried. The weight average molecularweight (Mw) of the resin particles was 3×105. A glass transition point(Tg) thereof was 38° C.

PREPARATION EXAMPLE 2 OF RESIN PARTTCT-E Preparation of Resin Particle(L-2)

A mixed solution of 12 g of Resin for Dispersion Stabilization (P-2) and177 g of Isopar H was heated to a temperature of 60° C. under nitrogengas stream with stirring. To the solution was added dropwise a mixedsolution of 40 g of methyl methacrylate, 60 g of methyl acrylate, 3 g ofMacromonomer (MA-5), 200 g of Isopar G and 1.0 g of AIVN over a periodof 2 hours, followed by stirring for 2 hours. Then, 0.5 g of AIVN wasadded to the reaction mixture and the mixture was heated to atemperature of 75° C., followed by reacting for 3 hours. After coolingthe reaction mixture, it was passed through a nylon cloth of 200 mesh.The resulting white dispersion was a latex having a polymerization rateof 99% and an average particle diameter of 0.38 μm. The weight averagemolecular weight (Mw) of the resin particles was 1×10⁵. A glasstransition point (Tg) thereof was 38° C.

PREPARATION EXAMPLES 3 TO 6 OF RESIN PARTICLE Preparation of ResinParticles (L-3) To (L-6)

Resin Particles (L-3) to (L-6) were prepared in the same manner as inPreparation Example 1 of Resin Particle expect that 11 g of Resin forDispersion Stabilization (P-4) was used in plane of 10 g of Resin forDispersion Stabilization (P-1), and Monomer (A) and Macromonomer (MA)shown in Table 3 below were used in place of vinyl acetate andMacromonomer (MA-1), respectively.

A polymerization rate of each of the resulting resin particles was in arange of from 93% to 98%, and an average particle diameter thereof wasin a range of from 0.35 μm to 0.04 μm with good monodispersity. The Mwof each of the resin particles was in a range of from 8×10⁴ to 1-10⁵.

                  TABLE 3                                                         ______________________________________                                        Prepara-                                                                             Resin                     Macro-  Tg of                                  tion Par-   monomer Resin                                                     Example ticle Monomer (A)  (MA) Particle                                    ______________________________________                                        3      L-3    Vinyl Acetate                                                                              80  g   MA-1  3 g 32° C.                        Vinyl Propionate 20 g                                                       4 L-4 Vinyl Acetate 95 g MA-16 4 g 43° C.                                Crotonic Acid 5 g                                                           5 L-5 Vinyl Acetate 90 g MA-6 4 g 45° C.                                 N-Vinylpyrrolidone 10 g                                                     6 L-6 Vinyl Acetate 82 g MA-9 5 g 35° C.                                 Vinylacetic Acid 8 g                                                          Vinyl Butyrate 10 g                                                       ______________________________________                                    

PREPARATION EXAMPLES 7 TO 15 OF RESTN PARTICLE Preparation of ResinParticles (L-7) to (L-15)

Resin Particles (L-7) to (L-15) were prepared in the same manner as inPreparation Example 2 of Resin Particle expect that 11 g of Resin forDispersion Stabilization (P-3) was used in pace of 12 g of Resin forDispersion Stabilization (P-2), and the compounds shown in Table 4 belowwere used in place of Monomer (A) (i.e., methyl methacrylate and methylacrylate), and Macromonomer (MA-5), respectively.

A polymerization rate of each of the resulting resin particles was in arange of from 95% to 99% and an average particle diameter thereof was ina range of from 0.38 μm to 0.45 μm with good monodispersity. The Mw ofeach of the resin particles was in a range of from 8×10⁴ to 2×10⁵.

                                      TABLE 4                                     __________________________________________________________________________    Preparation                                                                         Resin                      Tg of Resin                                    Example Particle Monomer (A) Macromonomer (MA) Particle                     __________________________________________________________________________    7     L-7 Methyl Methacrylate                                                                     50 g                                                                             MA-2 4.5 g                                                                              27° C.                                    Ethyl Acrylate 50 g                                                         8 L-8 Methyl Methacrylate 25 g MA-4 4 g 26° C.                           Methyl Acrylate 75 g                                                        9 L-9 Methyl Methacrylate 25 g MA-12 3 g 26° C.                          Methyl Acrylate 75 g                                                        10 L-10 Methyl Methacrylate 25 g MA-13 2.5 g 26° C.                      Methyl Acrylate 75 g                                                        11 L-11 Ethyl Methacrylate 45 g MA-8 3 g 24° C.                          Ethyl Acrylate 55 g                                                         12 L-12 Ethyl Methacrylate 60 g MA-16 4 g 28° C.                         Methyl acrylate 40 g                                                        13 L-13 Methyl Methacrylate 20 g MA-14 2.5 g 30° C.                      2-Cyanoethyl Acrylate  8 g                                                    Methyl Acrylate 72 g                                                        14 L-14 Vinyl Acetate 80 g MA-9 3 g 35° C.                               styrene 10 g                                                                  Vinyl Propionate 10 g                                                       15 L-15 Methyl Methacrylate 20 g MA-11 2.8 g 36° C.                      n-Propyl Methacrylate  5 g                                                     80 g                                                                     __________________________________________________________________________

PREPARATION EXAMPLES 16 TO 19 OP RESIN PARTICLE Preparation of ResinParticles (L-16) to (L-19)

Resin Particles (L-16) to (L-19) were prepared in the same manner as inPreparation Example 1 of Resin Particle expect for using Resins forDispersion Stabilization (P) and Macromonomers (MA) shown in Table 5below in place of Resin for Dispersion Stabilization (P-1) andMacromonomer (MA-1), respectively.

A polymerization rate of each of the resulting resin particles was in arange of from 97% to 98% and an average particle diameter thereof was ina range of form 0.3 μm to 0.4 μm with good monodispercity. The Mw ofeach of the resin particles was in a range of from 2×10⁵ to 3×10⁵, and aTg thereof was in a range of from 37° C. to 38° C.

                                      TABLE 5                                     __________________________________________________________________________    Resin for Dispersion Stabilization                                              #STR33##                                                                       -                                                                          Preparation                                                                         Resin                         x/y    Macromonomer                         Example Particle --Y (weight ratio) (MA)                                    __________________________________________________________________________      16 L-16                                                                                                                        97/3 MA-3 3 g                 - 17 L-17                                                                                                                     95/5 MA-15 2.5 g                                                              - 18 L-18                                                                     98/2 MA-10 2 g                                                                - 19 L-19                                                                     96/4 MA-6 3 g              __________________________________________________________________________

PREPARATION EXAMPLE 20 OF RESIN PARTICLE Preparation of ComparativeResin Particle (L-20)

Comparative Resin Particle (L-20) was prepared in the same manner as inPreparation Example 1 of Resin Particle expect for eliminating 4 g ofMacromonomer (MA-1). The resin particles had a polymerization rate of95% and an average particle diameter of 0.45 μm. The Mw of the resinparticles was 3×10⁵ and a Tg thereof was 37° C.

EXAMPLE 1

Preparation of Lithographic Printing Plate Precursor

A composition having the following component was placed in a paintshaker (manufactured by Toyo Seiki Co., Ltd.) together with glass beadsand dispersed for 60 minutes. Then, the glass beads were removed byfiltration to obtain a dispersion.

    ______________________________________                                        10% Aqueous Solution of Gelatin                                                                           120    g                                            Silica: Silysia 310 (manufactured 80 g                                        by Fuji Silysia Chemical Co., Ltd.)                                           20% Solution of Colloidal Silica: 40 g                                        Snowtex C (manufactured by Nissan                                             Chemical Industries, Ltd.)                                                    Fluorinated Alkyl Ester: FC 430 0.8 g                                         (manufactured by 3M Co.)                                                      Hardening Compound 0.24 g                                                     [CH.sub.2 ═CHSO.sub.2 CH.sub.2 CONH(CH.sub.2).sub.3 NHCOCH.sub.2                                           SO.sub.2 CH═CH.sub.2 ]                   Water 54 g                                                                  ______________________________________                                    

On a support of ELP-1X Type Master (manufactured by Fuji Photo Film Co.,Ltd.) used as an electrophotographic lithographic printing plateprecursor for small-scale commercial printing, the above-describedcomposition was coated using a wire bar and dried at 100° C. for 10minutes to form an image receiving layer having a coating amount of 18g/m², thereby obtaining a lithographic printing plate precursor.

The Bekk smoothness of the surface of the printing plate precursor was250 (second/10 ml), and the contact angle with water thereof was 0degree.

The Bekk smoothness of the printing plate precursor was determined usinga Bekk smoothness tester (manufactured by Kumagaya Riko Co., Ltd.) underthe condition of an air volume of 10 ml as described hereinbefore.

The contact angle of the image receiving layer with water was determinedby placing 2 μl of distilled water on the surface of the printing plateprecursor and measuring the surface contact angle (degree) after 30seconds using a surface contact angle meter (CA-D, manufactured by KyowaKaimen Kagaku Co., Ltd.) as described hereinbefore.

Preparation of Oil-Based Ink (IK-1) Ten grams of dodecylmethacrylate/acrylic acid copolymer (copolymerization ratio: 95/5 byweight), 10 g of Alkali Blue and 30 g of Shellsol 71 were placed in apaint shaker (manufactured by Toyo Seiki Co., Ltd.) together with glassbeads and dispersed for 4 hours to obtain a fine dispersion of AlkaliBlue.

Fifty grams (as a solid basis) of Resin Particle (L-1) according toPreparation Example 1 of Resin Particle, 18 g of the above-describedAlkali Blue dispersion, 10 g of tetradecyl alcohol (FOC-1400manufactured by Nissan Chemical Industries, Ltd.) and 0.16 g ofoctadecene-maleic acid monooctadecylamide copolymer were diluted withone liter of Isopar G, thereby obtaining blue oil-based ink.

A servo plotter (DA8400, manufactured by Graphtech Co.) able to write anoutput from a personal computer was converted so that an ink dischargehead as shown in FIG. 2 was mounted on a pen plotter section, and thelithographic printing plate precursor described above was placed on acounter electrode positioned at a distance of 1.5 mm from the inkdischarge head. Ink jet printing was performed on the lithographicprinting plate precursor using Oil-Based Ink (IK-1) described above tomake a plate. Successively, heating was carried out for 20 seconds usinga Ricoh Fuser Model 592 (manufactured by Ricoh Co., Ltd.) so as toadjust the surface temperature of the ink image formed to 70° C.,thereby sufficiently fixing the image area.

The image on the resulting printing plate was visually observed under anoptical microscope of 200 magnifications. As a result, the image had noproblem, fine lines and fine letters were good, defect such as blur,disappearance or spread was not recognized, and contamination was notobserved in the non-image area.

The printing plate was subjected to printing using, as dampening water,a solution prepared by diluting SLM-OD (manufactured by Mitsubishi PaperMills, Ltd.) 10 times with water, Oliver 94 Type (manufactured bySakurai Seisakusho Co., Ltd.) as a printing machine, and a black ink foroffset printing.

As a result, more than 1,000 sheets of prints having clear imageswithout the occurrence of background stain were obtained.

Using the above-described ink jet printer, an ink ejection test wasconducted. As a result, it was found that stable ink jet was obtainedeven after the lapse of 600 hours.

The oil-based ink of the present invention stored at room temperaturefor 6 months showed no formation of aggregates, and gave stable ink jetin the ink ejection test same as described above.

When a printing plate was prepared using the oil- based ink stored for 6months and printing was conducted in the same manner as above, more than1,000 sheets of prints having clear images without the occurrence ofbackground stain were obtained.

Furthermore, the redispersibility of the oil-based ink was evaluatedunder enforced conditions. Specifically, the discharge head used in theabove-described printer was filled with the ink, taken away and allowedto stand at 35° C. for 3 days. Then, the discharge head was immersed inIsopar G for 3 minutes, followed by mild stirring. Thereupon, Oil-BasedInk (IK-1) was all removed from the inside of the slit. This isconsidered to be caused by that the Oil-Based Ink (IK-1) adhered to theleading edge of the slit of the discharge head in the non-fluid stateduring the standing was easily redispersed upon the solvation with thedispersing medium.

From these results it can be seen that the oil-based ink of the presentinvention is excellent in stability of ink discharge and forms clearimages without the occurrence of stain even when it has beencontinuously employed for a long period of time, and provides a printingplate having good press life.

COMPARATIVE EXAMPLE A

Comparative Example A was conducted in the same manner as in Example 1with the exception that Oil-Base Ink (IKR-1) for Comparison describedbelow was employed in place of Oil-Based Ink (IK-1) used in Example 1 toprepare a lithographic printing plate. Oil-Based Ink (IKR-i) forComparison Oil-Base Ink (IKR-1) for Comparison was prepared in the samemanner as in Oil-Based Ink (IK-1) with the exception that 50 g (as asolid basis) of Comparative Resin Particle (L-20) was employed in placeof Resin Particle (L1) used in Oil-Based Ink (IK-1).

When the lithographic printing plate obtained in Comparative Example Adescribed above was subjected to the printing in the same manner as inExample 1, more than 1,000 sheets of prints having clear images withoutthe occurrence of background stain were obtained.

However, in the ink ejection test, Oil-Based Ink (IKR-1) for Comparisonbecame unstable in ink discharge after the lapse of about 100 hours.Further, in Oil-Based Ink (IKR-1) for Comparison stored for 6 months,coagulated precipitates were deposited and not redispersed even onshaking in the dispersing medium.

EXAMPLE 2

Preparation of Lithographic Printing Plate Precursor

A composition having the following content was placed in a paint shaker(manufactured by Toyo Seiki Co., Ltd.) together with glass beads anddispersed for 60 minutes. Then, the glass beads were removed byfiltration to obtain dispersion.

    ______________________________________                                        10% Aqueous Solution of Gelatin                                                                           100    g                                            Silica: Silysia 310 (manufactured by 7 g                                      Fuji Silysia Chemical Co., Ltd.)                                              10% Solution of Aluminasol 200 41 g                                           (manufactured by Nissan Chemical                                              Industries, Ltd.)                                                             Fluorinated Alkyl Ester: FC 430 0.8 g                                         (manufactured by 3M Co.)                                                      Hardening Compound 0.30 g                                                     [CH.sub.2 ═CHSO.sub.2 CH.sub.2 CONH(CH.sub.2).sub.3 NHCOCH.sub.2                                           SO.sub.2 CH═CH.sub.2 ]                   Water 54 g                                                                  ______________________________________                                    

On a support of ELP-II Type Master (manufactured by Fuji Photo Film Co.,Ltd.) used as an electrophotographic lithographic printing plateprecursor for small-scale commercial printing, the above-describedcomposition was coated using a wire bar and dried at 100° C. for 10minutes to form an image-receiving layer having a coating amount of 18g/m², thereby obtaining a lithographic printing plate precursor. TheBeck smoothness of the surface of the image receiving layer was 200(second/10 ml), and the contact angle with water thereof was 0 degree.Preparation of Oil-Based Ink (IK-2)

Ten grams of poly(dodecyl methacrylate), 10 g of nigrosine and 30 g ofIsopar H were placed in a paint shaker (manufactured by Toyo Seiki Co.,Ltd.) together with glass beads, and dispersed for 4 hours to obtain afine black dispersion of nigrosine.

Fifty grams (as a solid basis) of Resin Particle (L-2) according toPreparation Example 2 of Resin Particle, 35 g of the above-describednigrosine dispersion and 0.08 g of octadecyl vinyl- ether-maleic acidmonododecylamide copolymer were diluted with one liter of Isoper G,thereby preparing black oil-based ink.

Using the printing plate precursor and Oil-Based Ink (IK-2) describedabove, plate-making was conducted to prepare a printing plate and offsetprinting was performed in the same manner as in Example 1.

The resulting prints had clear images without the occurrence of stain inthe non-image area similar to the prints obtained in Example 1, and thepress life of the printing plate was as good as 1,000 sheets or more.

Further, with Oil-Based Ink (IK-2), the ink ejection test for 600 hoursand the redispersibility test under enforced conditions were carried outin the same manner as in Example 1. Good results similar to those inExample 1 were obtained.

EXAMPLE 3

Using wood free paper having a basis weight of 100 g/m² as a substrate,one surface of the substrate was coated with a coating for a backcoatlayer having the composition shown below using a wire bar to form thebackcoat layer having a dry coating amount of 12 g/m². The Bekksmoothness of the surface of the backcoat layer was adjusted to about 50(second/10 ml) by a calender treatment.

Coating for Backcoat Layer

    ______________________________________                                        Kaolin (50% aqueous dispersion)                                                                        200    parts                                           Polyvinyl Alcohol (10% aqueous solution) 60 parts                             SBR Latex (solid content: 50%, Tg: 0° C.) 100 parts                    Melamine Resin 5 parts                                                        (solid content: 80%, Sumirez Resin SR-613)                                  ______________________________________                                    

The other surface of the substrate was coated with each of Coatings A toG for an under layer having the composition shown in Table 6 below usinga wire bar to form the under layer having a dry coating amount of 10g/m². Then, a calender treatment was conducted so that the Bekksmoothness of the under layer is adjusted to about 1,500 (second/10 ml).The resulting seven water-resistant supports using Coatings A to G weredesignated Support Sample Nos. 1 to 7, respectively.

                  TABLE 6                                                         ______________________________________                                                Coating Composition                                                     Coating (% by weight on solid basis) Support                                for Under                                                                             Carbon                  Melamine                                                                              Sample                                  Layer Black Clay SBR Latex Resin No.                                        ______________________________________                                        A       0        60     36      4       1                                       B 3 57 36 4 2                                                                 C 5.4 54.6 36 4 3                                                             D 7.2 52.8 36 4 4                                                             E 9 51 36 4 5                                                                 F 15 45 36 4 6                                                                G 30 30 36 4 7                                                              ______________________________________                                         Coating for Under Layer                                                       Carbon Black (30% aqueous dispersion)                                         Clay (50% aqueous dispersion)                                                 SBR Latex (solid content: 50%, Tg: 25° C.)                             Melamine Resin (solid content: 80%, Sumirez Resin SR613)                 

The components were mixed according to the amounts shown in Table 6above, and water was added thereto to adjust the total solid content to25%, thereby obtaining Coatings A to G for the under layer.

Specific Electric Resistance of Under Layer

The specific electric resistance of the under layer was measured in thefollowing manner.

Each of Coatings A to G for the under layer was coated on a sufficientlydegreased and washed stainless plate to prepare a layer having a drycoating amount of 10 g/m². The specific electric resistance of theresulting seven samples were measured by a three terminal process havinga guard electrode according to JIS K-6911. The results are shown inTable 7 below.

                  TABLE 7                                                         ______________________________________                                        Coating for   Specific Electric                                                 Under Layer Resistance (Ωcm)                                          ______________________________________                                        A              2 × 10.sup.12                                              B  1 × 10.sup.11                                                        C 4 × 10.sup.9                                                          D 1 × 10.sup.8                                                          E 7 × 10.sup.4                                                          F 5 × 10.sup.3                                                          G 4 × 10.sup.3                                                        ______________________________________                                    

Preparation of Lithographic Printing Plate Precursor

On the under layer of each of Support Sample Nos. 1 to 7 was coated adispersion having the same composition as described in Example 1 to forman image receiving layer having a dry coating amount of 6 g/m², wherebyLithographic Printing Plate Precursor Sample Nos. 1 to 7 were prepared.The Bekk smoothness of the surface of each printing plate precursor wasin a range of from 200 to 230 (second/10 ml), and the contact angle withwater thereof was 5 degrees.

Using the lithographic printing plate precursors thus prepared, platemaking was conducted with Oil-Based Ink (IK-1) in the same manner as inExample 1. The counter electrode was electrically connected with theunder layer provided directly under the image receiving layer of theprecursor using silver paste at the plate making.

Then, the printing plates were subjected to printing using a fullyautomatic printing machine (AM-2850 manufactured by AM Co., Ltd.)provided with a solution prepared by diluting ELP-E2 (manufactured byFuji Photo Film Co., Ltd.) 10 times with distilled water, as dampeningwater, in a dish for dampening water thereof and a black ink for offsetprinting.

The properties of the printing plates and the prints obtained wereevaluated with respect to the points shown below. The results are shownin Table 8 below.

                  TABLE 8                                                         ______________________________________                                        Lithographic                                                                    Printing Plate Support Image Quality Image                                    Precursor Sample of Printing Quality of Press                                 Sample No. No. Plate.sup.1) Print.sup.2) Life.sup.3)                        ______________________________________                                        1        1        Poor        Poor      50                                      2 2 Poor Poor  100                                                            3 3 Good Good 1500                                                            4 4 Very Good Very Good 3000                                                  5 5 Very Good Very Good 3000                                                  6 6 Very Good Very Good 3000                                                  7 7 Very Good Very Good 3000                                                ______________________________________                                    

1) Image Quality of Printing Plate

Images on the printing plate were visually observed under an opticalmicroscope of 200 magnifications. The results were evaluated as follows:

Very good: Completely no problem in images, very good fine lines andfine letters

Good: No problem in images, good fine lines and fine letters

Poor: Disappearance or blur of fine lines and fine letters

2) Image Quality of Print

The images of the print were evaluated in the same manner as the imagequality of the printing plate described above. The image quality of theprint was the same as that of the printing plate in each sample.

3) Press Life

The number of prints obtained was counted until background stain ordisappearance of image was visually recognized on the print.

With Lithographic Printing Plate Precursor Sample Nos. 4 to 7 whereinthe support having an under layer of a small specific electricalresistance of 10⁸ to 10³ Ωcm is used, the images have no problem at all,reproduction of fine lines and fine letters is very good, and press lifeis also excellent. On the contrary, with Lithographic Printing PlatePrecursor Sample Nos. 1 and 2 wherein the support having an under layerof a large specific electrical resistance of 10¹² to 10¹¹ μcm is used,disappearance or blur of image occurs on the printing plate. Due to theblur, the resin layer of the image becomes thin and as a result, presslife is poor.

These results indicate that the higher the electroconductivity of theunder layer provided directly under the image receiving layer, thebetter the image quality of printing plate and the image quality ofprint.

EXAMPLES 4 TO 20

Plate making and printing were conducted in the same manner as inExample 1 with the exception that each oil-based ink described in Table9 shown below was used in place of Oil-Based Ink (IK-1). The oil-basedink used were prepared in the same manner as in Oil-Based Ink (IK-1)except for using 50 g (as a solid basis) of Resin Particles (L)described in Table 9 shown below in place of Resin Particle (L-1),respectively.

                  TABLE 9                                                         ______________________________________                                        Example      Oil-Based Ink                                                                            Resin Particle (L)                                    ______________________________________                                         4           IK-3       L-8                                                      5 IK-4  L-3                                                                   6 IK-5  L-4                                                                   7 IK-6  L-5                                                                   8 IK-7  L-6                                                                   9 IK-8  L-7                                                                  10 IK-9  L-9                                                                  11 IK-10 L-10                                                                 12 IK-11 L-11                                                                 13 IK-12 L-12                                                                 14 IK-13 L-13                                                                 15 IK-14 L-14                                                                 16 IK-15 L-15                                                                 17 IK-16 L-16                                                                 18 IK-17 L-18                                                                 19 IK-18 L-19                                                                 20 IK-19 L-17                                                               ______________________________________                                    

It has been found that the images on each printing plate had goodqualities similar to those in Example 1, and the press life of eachprinting plate was more than 1,000 sheets.

Further, the ink ejection test for 600 hours and the redispersibilitytest under enforced conditions were performed in the same manner as inExample 1. Each oil-based ink exhibited good results similar to or morethan those of Oil-Based Ink (IK-1) used in Example 1.

EXAMPLE 21

Preparation of Water-Resistant Support

Using wood free paper having a basis weight of 100 g/m² as a substrate,one. surface of the substrate was coated with a coating for an underlayer having the composition shown below using a wire bar to form theunder layer having a dry coating amount of 10 g/m². The Bekk smoothnessof the surface of the under layer was 150 (second/10 ml), and adjustedto 1,500 (second/10 ml) by a calender treatment.

Coating for Under Layer

    ______________________________________                                        Silica gel              10     parts                                            SBR Latex 92 parts                                                            (50% aqueous dispersion, Tg: 25° C.)                                   Clay (45% aqueous dispersion) 110 parts                                       Melamine (80% aqueous solution) 5 parts                                       Water 191 parts                                                             ______________________________________                                    

The other surface of the substrate was coated with a coating for abackcoat layer having the composition shown below using a wire bar toform the backcoat layer having a dry coating amount of 12 g/m². Then, acalender treatment was conducted so that the Bekk smoothness of thebackcoat layer is adjusted to about 50 (second/10 ml). Coating forBackcoat Layer

    ______________________________________                                        Kaolin (50% aqueous dispersion)                                                                       200    parts                                            Polyvinyl Alcohol 60 parts                                                    (10% aqueous solution)                                                        SBR Latex 100 parts                                                           (solid content: 49%, Tg 0° C.)                                         Primary Condensation Product of 5 parts                                       Melamine Resin (solid content: 80%,                                           Sumirez Resin SR-613)                                                       ______________________________________                                    

Preparation of Lithographic Printing Plate Precursor

A composition having the following component was placed in a paintshaker together with glass beads and dispersed for 80 minutes. Then, theglass beads were removed by filtration to obtain a dispersion.

    ______________________________________                                        Silica: Silysia 445 (manufactured by                                                                   40     g                                               Fuji Silysia Chemical Co., Ltd.)                                              20% Solution of Colloidal Silica: 200 g                                       Snowtex C (manufactured by Nissan                                             Chemical Industries, Ltd.)                                                    50% Dispersion of Clay 40 g                                                   10% Solution of Polyvinyl Alcohol: 120 g                                      PVA-117 (manufactured by Kuraray                                              Co., Ltd.)                                                                    Melamine Resin 2.0 g                                                          Ammonium Chloride 0.2 g                                                       Water 50 g                                                                  ______________________________________                                    

The dispersion was coated on the under layer of the above-describedwater-resistant support using a wire bar and dried to form an imagereceiving layer having a coating amount of 20 g/m², thereby obtaining alithographic printing plate precursor. The Bekk smoothness of thesurface of the printing plate precursor was 150 (second/10 ml), and thecontact angle with water thereof was 0 degree.

The printing plate precursor was subjected to plate making to prepare alithographic printing plate and printing in the same manner as inExample 1 except for using Oil-Based Ink (IK-20) having the compositionshown below in place of Oil-Based Ink (IK-1) employed in Example 1.

Preparation of Oil-Based Ink (IK-20)

A mixture of 500 g of a white dispersion of Resin Particle (L-5)according to Preparation Example 5 of Resin Particle and 7.5 g ofSumikaron Black was heated to a temperature of 100° C. and stirred for 6hours under heating. After cooling to room temperature, the mixture waspassed through a nylon cloth of 200 mesh to remove the remaining dye,thereby obtaining a black resin dispersion having an average particlediameter of 0.40 Rm.

Then, 250 g of the above-described black resin dispersion, 0.10 g ofCharge Control Agent (CD-3) shown below and 10 g of hexadecyl alcohol(FOC-1600 manufactured by Nissan Chemical Industries, Ltd.) were dilutedwith one liter of Isopar G, thereby preparing black oil-based ink.

Charge Control Agent CD-3 ##STR38##

The prints thus-obtained had clear images without the occurrence ofstain in the non-image area similar to the prints obtained in Example 1,and the press life of the printing plate was good as 1,000 sheets ormore.

Further, with Oil-Based Ink (IK-20), the ink ejection test for 600 hoursand the redispersibility test under enforced conditions were performedin the same manner as in Example 1. As a result, Oil-Based Ink (IK-20)exhibited good results similar to those of Oil-Based Ink (IK-1).

EXAMPLE 22

Plate-making and printing were carried out in the same manner as inExample 1 except for using Oil-Based Ink (IK-21) having the compositionshown below in place of Oil- Based Ink (IK-1) employed in Example 1.

Preparation of Oil-Based Ink (IK-21)

A mixture of 300 g of a white dispersion of Resin Particle (L-6)according to Preparation Example 6 of Resin Particle and 5 g of VictoriaBlue B was heated to a temperature of 100° C. and stirred for 4 hoursunder heating. After cooling to room temperature, the mixture was passedthrough a nylon cloth of 200 mesh to remove the remaining dye, therebyobtaining a blue resin dispersion having an average particle diameter of0.38 μm.

Then, 260 g of the above-described blue resin dispersion and 0.10 g ofzirconium naphthenate were diluted with one liter of Shellsol 71,thereby preparing blue oil-based ink.

The prints thus-obtained had clear images without the occurrence ofstain in the non-image area similar to the prints obtained in Example 1,and the press life of the printing plate was good as 1,000 sheets ormore.

Further, with Oil-Based Ink (IK-21), the ink ejection test for 600 hoursand the redispersibility test under enforced conditions were performedin the same manner as in Example 1. As a result, Oil-Based Ink (IK-21)exhibited good results similar to those of Oil-Based Ink (IK-1).

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modification can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A method for preparing a printing plate by an inkjet process consisting essentially of discharging dropwise an oil-basedink using electrostatic attraction from a head having a dischargeelectrode on a lithographic printing plate precursor positioned betweenthe discharge electrode and a counter electrode to form an image,wherein the lithographic printing plate precursor comprises awater-resistant support having provided thereon an image-receiving layerhaving a lithographically printable hydrophilic surface for forming theimage, the water resistant support has a specific electric resistance of10¹⁰ Ωcm or less at least at an area directly under the image receivinglayer, the oil-based ink comprises positively or negatively chargedelectroscopic resin particles dispersed in a nonaqueous carrier liquidhaving an electric resistance of 10⁹ Ωcm or more and a dielectricconstant of 3.5 or less, and the resin particles dispersed are copolymerresin particles obtained by polymerization granulation of a solutioncomprising (i), (ii) and (iii):(i) at least one monofunctional monomer(A) which is soluble in a nonaqueous solvent that is at least misciblewith the nonaqueous carrier liquid and becomes insoluble in thenonaqueous solvent by polymerization; (ii) at least one monofunctionalmacromonomer (MA) having a weight average molecular weight of 2×10⁴ orless in which a polymerizable double bond group represented by theformula (II) shown below is connected with only one terminal of the mainchain of a polymer comprising a repeating unit corresponding to amonomer and represented by the formula (I) shown below; ##STR39##wherein V⁰ represents --COO--, --OCO--, --(CH₂)_(r) COO--, --(CH₂)_(r)OCO--, --O--, --SO₂ --, --CONHCOO--, --CONHCONH--, --CON(D¹¹)--, --SO₂N(D¹¹)-- or a phenylene group, in which D¹¹ represents a hydrogen atomor a hydrocarbon group having from 1 to 22 carbon atoms, and rrepresents an integer of from 1 to 4; a¹ and a², which may be the sameor different, each represents a hydrogen atom, a halogen atom, a cyanogroup, a hydrocarbon group, --COO--D¹² or --COO--D¹² linked through ahydrocarbon group, in which D¹² represents a hydrogen atom or ahydrocarbon group which may be substituted; D⁰ represents a hydrocarbongroup having from 8 to 22 carbon atoms or a substituent having a totalnumber of atoms of 8 or more, provided that hydrogen atoms directlyattached to a carbon or nitrogen atom are excluded from the number,represented by the following formula (Ia):

    .paren open-st.A.sup.1 -B.sup.1 .paren close-st..sub.m .paren open-st.A.sup.2 -B.sup.2 .paren close-st..sub.n D.sup.21  (Ia)

wherein D²¹ represents a hydrogen atom or a hydrocarbon group havingfrom 1 to 22 carbon atoms; B¹ and B², which may be the same ordifferent, each represents --O--, --CO--, --CO₂ --, --OCO--, --SO₂ --,--N(D²²)--, --CON(D²²)--, or --N(D²²)CO--, in which D²² has the samemeaning as defined for D²² above; A¹ and A², which may be the same ordifferent, each represents at least one group selected from the groupconsisting of a group represented by the formula (Ib) shown below and ahydrocarbon group having from 1 to 18 carbon atoms, which may besubstituted, provided that, in the case of two or more, it represents acombination of the group represented by the formula (Ib) and/or thehydrocarbon group: ##STR40## wherein B³ and B⁴, which may be the same ordifferent, each has the same meaning as defined for B¹ and B² above; A⁴represents a hydrocarbon group having from 1 to 18 carbon atoms whichmay be substituted; D²³ has the same meaning as defined for D²¹ above;and m, n and p, which may be the same or different, each represents aninteger of from 0 to 4, provided that m and n are not 0 at the sametime; ##STR41## wherein V¹ represents --COO--, --CONHCOO--,--CONHCONH--, --CONH-- or a phenylene group; and b¹ and b², which may bethe same or different, each has the same meaning as defined for al or ain the formula (I);(iii) at least one resin for dispersion stabilization(P) which is soluble in the nonaqueous solvent and comprises a copolymercomponent represented by the formula (III) shown below: ##STR42##wherein R¹ represents an alkyl group having from 10 to 32 carbon atomsor an alkenyl group having from 10 to 32 carbon atoms; d¹ represents ahydrogen atom or an alkyl group having from 1 to 4 carbon atoms; X¹ andX², which may be the same or different, each has the same meaning asdefined for V¹ in the formula (I); W represents a group connecting X¹and X² and comprising at least one of a carbon atom and a hetero atomselected from an oxygen atom, a sulfur atom, a silicon atom and anitrogen atom; e¹, e², f¹ and f², which may be the same or different,each has the same meaning as defined for a¹ or a² in the formula (I);and x and y each represents a weight ratio of each repeating unit, xrepresents a number of from 90 to 99, y represents a number from 10to
 1. 2. The method of claim 1, wherein the monofunctional monomer (A)is a monomer represented by the following formula (IV): ##STR43##wherein T¹ represents --COO--, --OCO--, --CH₂ OC--, --CH₂ COO--, --O--,--CONHCOO--, --CONHOCO--, --SO₂₋₋, --CON(W¹)--, --SO₂ N(W¹)--, or aphenylene group, wherein W¹ represents a hydrogen atom or an aliphaticgroup having from 1 to 8 carbon atoms which may be substituted; D¹represents a hydrogen atom or an aliphatic group having from 1 to 6carbon atoms which may be substituted; and g¹ and g², which may be thesame or different, each represents a hydrogen atom, a halogen atom, acyano group, a hydrocarbon group, --COO--D¹² -- or --COO--D¹² -- linkedthrough a hydrocarbon groupwherein D¹² represents a hydrogen atom or ahydrocarbon group which may be substituted[)].
 3. The method of claim 1,wherein the monofunctional macromonomer (MA) is a macromonomerrepresented by the following formula (V): ##STR44## wherein symbolsother than z have the same meanings as defined for those in the formulas(I) and (II), respectively; and z represents a single bond or aconnecting group.
 4. The method of claim 1, wherein the repeating unitrepresented by the formula (I) is present in the macromonomer (MA) in anamount of 60% by weight or more of the total amount of the repeatingunits contained therein.
 5. The method of claim 1, wherein themacromonomer (MA) has a weight average molecular weight of from 1×10³ to2×10⁴.
 6. The method of claim 1, wherein the amount of themonofunctional macromonomer (MA) is from 0.1% to 20% by weight based onthe amount of the monomer (A).
 7. The method of claim 1, wherein theamount of the resin for dispersion stabilization (P) is from 3 to 25parts by weight of the total amount of the monomers.
 8. The method ofclaim 1, wherein the oil-based ink further comprises a coloringmaterial.
 9. The method for the preparation of a printing plate by anink jet process as claimed in claim 1, wherein the water-resistantsupport is a support having a specific electric resistance of 10.sup.Ωcm or less as a whole of the support.